diff --git "a/YIM2UL2ET/BFS/13\354\260\250\354\213\234 - BOJ 7569.cpp" "b/YIM2UL2ET/BFS/13\354\260\250\354\213\234 - BOJ 7569.cpp"
new file mode 100644
index 0000000..4db562f
--- /dev/null
+++ "b/YIM2UL2ET/BFS/13\354\260\250\354\213\234 - BOJ 7569.cpp"	
@@ -0,0 +1,50 @@
+#include <iostream>
+#include <vector>
+#include <queue>
+
+struct idx {int z, y, x;};
+
+int main(void)
+{
+    std::ios_base::sync_with_stdio(false);
+    std::cin.tie(NULL);
+
+    int m, n, h, res = 0, non = 0;
+    std::vector <idx> offset = {{1, 0, 0}, {-1, 0, 0}, {0, 1, 0}, {0, -1, 0}, {0, 0, 1}, {0, 0, -1}};
+    std::queue <idx> que[2];
+    bool curQueue = false;
+
+    std::cin >> n >> m >> h;
+    int box[h][m][n];
+
+    for (int z = 0; z < h; z++) {
+        for (int y = 0; y < m; y++) {
+            for (int x = 0; x < n; x++) {
+                std::cin >> box[z][y][x];
+                if (box[z][y][x] == 1) que[curQueue].push({z, y, x});
+                else if (box[z][y][x] == 0) non++;
+            }
+        }
+    }
+
+    while (!que[curQueue].empty() && non > 0) {
+        while (!que[curQueue].empty()) {
+            int z = que[curQueue].front().z, y = que[curQueue].front().y, x = que[curQueue].front().x;
+            for (idx set : offset) {
+                int zz = z + set.z, yy = y + set.y, xx = x + set.x;
+                if (zz >= 0 && zz < h && yy >= 0 && yy < m && xx >= 0 && xx < n && box[zz][yy][xx] == 0) {
+                    box[zz][yy][xx] = 1, non--;
+                    que[!curQueue].push({zz, yy, xx});
+                }
+            }
+            que[curQueue].pop();
+        }
+        curQueue = !curQueue;
+        res++;
+    }
+
+    if (non > 0) std::cout << -1;
+    else std::cout << res;
+    
+    return 0;
+}
\ No newline at end of file
diff --git a/YIM2UL2ET/README.md b/YIM2UL2ET/README.md
index c5601a7..2431e6c 100644
--- a/YIM2UL2ET/README.md
+++ b/YIM2UL2ET/README.md
@@ -12,4 +12,7 @@
 | 08차시 | 2024.03.04 |  재귀  | [BOJ 10994](https://www.acmicpc.net/problem/10994)  | [BOJ 10994 풀이](https://github.com/AlgoLeadMe/AlgoLeadMe-7/pull/27) |
 | 09차시 | 2024.03.07 |  임의 정밀도 / 큰 수 연산 && 재귀  | [BOJ 1914](https://www.acmicpc.net/problem/1914)  | [BOJ 1914 풀이](https://github.com/AlgoLeadMe/AlgoLeadMe-7/pull/29) |
 | 10차시 | 2024.03.10 |  스택  | [BOJ 1406](https://www.acmicpc.net/problem/1406)  | [BOJ 1406 풀이](https://github.com/AlgoLeadMe/AlgoLeadMe-7/pull/31) |
+| 11차시 | 2024.03.18 |  스택  | [BOJ 1918](https://www.acmicpc.net/problem/1918)  | [BOJ 1918 풀이](https://github.com/AlgoLeadMe/AlgoLeadMe-7/pull/36) |
+| 12차시 | 2024.03.28 |  비트마스킹  | [BOJ 11723](https://www.acmicpc.net/problem/11723)  | [BOJ 11723 풀이](https://github.com/AlgoLeadMe/AlgoLeadMe-7/pull/39) |
+| 13차시 | 2024.04.01 |  BFS  | [BOJ 7569](https://www.acmicpc.net/problem/7569)  | [BOJ 7569 풀이](https://github.com/AlgoLeadMe/AlgoLeadMe-7/pull/42) |
 ---
diff --git "a/YIM2UL2ET/\353\271\204\355\212\270\353\247\210\354\212\244\355\202\271/12\354\260\250\354\213\234 - BOJ 11723.cpp" "b/YIM2UL2ET/\353\271\204\355\212\270\353\247\210\354\212\244\355\202\271/12\354\260\250\354\213\234 - BOJ 11723.cpp"
new file mode 100644
index 0000000..c7b96fd
--- /dev/null
+++ "b/YIM2UL2ET/\353\271\204\355\212\270\353\247\210\354\212\244\355\202\271/12\354\260\250\354\213\234 - BOJ 11723.cpp"	
@@ -0,0 +1,36 @@
+#include <iostream>
+
+int main(void)
+{
+    std::ios_base::sync_with_stdio(false);
+    std::cin.tie(NULL);
+    std::cout.tie(NULL);
+
+    int n, k, bits = 0;
+    std::string command;
+    
+    std::cin >> n;
+    for (int i = 0; i < n; i++) {
+        std::cin >> command;
+        if (command == "add") {
+            std::cin >> k;
+            bits |= (1<<k);
+        }
+        else if (command == "remove") {
+            std::cin >> k;
+            bits &= ~(1<<k);
+        }
+        else if (command == "check") {
+            std::cin >> k;
+            if (bits & (1<<k)) std::cout << "1\n";
+            else std::cout << "0\n";
+        }
+        else if (command == "toggle") {
+            std::cin >> k;
+            bits ^= (1<<k);
+        }
+        else if (command == "all") bits = (1<<21)-1;
+        else bits = 0;
+    }
+    return 0;
+}
\ No newline at end of file
diff --git "a/YIM2UL2ET/\354\212\244\355\203\235/11\354\260\250\354\213\234 - BOJ 1918.cpp" "b/YIM2UL2ET/\354\212\244\355\203\235/11\354\260\250\354\213\234 - BOJ 1918.cpp"
new file mode 100644
index 0000000..0437fb6
--- /dev/null
+++ "b/YIM2UL2ET/\354\212\244\355\203\235/11\354\260\250\354\213\234 - BOJ 1918.cpp"	
@@ -0,0 +1,43 @@
+#include <iostream>
+#include <stack>
+
+int main(void)
+{
+    char ch;
+    std::stack <char> stk;
+    std::string res;
+
+    ch = getchar();
+    while (ch != '\n') {
+        if (ch == '+' || ch == '-') {
+            while(!stk.empty() && stk.top() != '(') {
+                res.push_back(stk.top());
+                stk.pop();
+            }
+            stk.push(ch);
+        }
+        else if (ch == '*' || ch == '/') {
+            if (!stk.empty() && (stk.top() == '*' || stk.top() == '/')) {
+                res.push_back(stk.top());
+                stk.pop();
+            }
+            stk.push(ch);
+        }
+        else if (ch == ')') {
+            while (!stk.empty() && stk.top() != '(') {
+                res.push_back(stk.top());
+                stk.pop();
+            }
+            if (!stk.empty()) stk.pop();
+        }
+        else if (ch == '(') stk.push(ch);
+        else res.push_back(ch);
+        ch = getchar();
+    }
+    while (!stk.empty()) {
+        res.push_back(stk.top());
+        stk.pop();
+    }
+    std::cout << res;
+    return 0;
+}
\ No newline at end of file