diff --git a/dhlee777/README.md b/dhlee777/README.md
index 2cbf92f..16a6955 100644
--- a/dhlee777/README.md
+++ b/dhlee777/README.md
@@ -5,6 +5,7 @@
 | 1차시 | 2024.03.12 |  BFS  | [숨바꼭질](https://www.acmicpc.net/problem/1697)  | [#4](https://github.com/AlgoLeadMe/AlgoLeadMe-8/pull/4)|
 | 2차시 | 2024.03.18 |   DP  | [쉬운계단수](https://www.acmicpc.net/problem/10844) | [#8](https://github.com/AlgoLeadMe/AlgoLeadMe-8/pull/8)|
 | 3차시 | 2024.03.23 |   union-find  | [집합의 표현](https://www.acmicpc.net/problem/1717) | [#14](https://github.com/AlgoLeadMe/AlgoLeadMe-8/pull/14)|
+| 4차시 | 2024.03.25 |   BFS  | [바이러스](https://www.acmicpc.net/problem/2606) | [#17](https://github.com/AlgoLeadMe/AlgoLeadMe-8/pull/17)|
 
 
 
diff --git "a/dhlee777/bfs/\353\260\224\354\235\264\353\237\254\354\212\244.cpp" "b/dhlee777/bfs/\353\260\224\354\235\264\353\237\254\354\212\244.cpp"
new file mode 100644
index 0000000..d81f922
--- /dev/null
+++ "b/dhlee777/bfs/\353\260\224\354\235\264\353\237\254\354\212\244.cpp"
@@ -0,0 +1,81 @@
+
+//*ù��° Ǯ��(bfs �̿�)
+#include<iostream>
+#include<vector>
+#include<queue>
+using namespace std;
+vector<int>com_edge[101];    //��ǻ�Ͱ��� ������ ������ �����ϴ� ����������
+int visited[101];   //������ ��ǻ������ Ȯ���ϱ����� �迭
+queue<int> q;
+int coun = 0;
+void bfs(int a) {     //bfs �� ���� �Լ�
+	q.push(a);
+	visited[a] = 1;
+	while (!q.empty()) {
+		int com = q.front();
+		q.pop();
+		for (int i = 0; i < com_edge[com].size(); i++) {
+			int com_linked = com_edge[com][i];
+			if (!visited[com_linked])
+			{
+				q.push(com_linked);
+				coun++;            //�湮�������� ����� ��ǻ���ϰ�� ī��Ʈ
+				visited[com_linked] = 1;
+			}
+		}
+	}
+
+}
+int main(void) {
+	ios_base::sync_with_stdio(false);
+	cin.tie(NULL);
+	int com_num, edge, a, b;
+	cin >> com_num >> edge;
+	for (int i = 0; i < edge; i++) {
+		cin >> a >> b;
+		com_edge[a].push_back(b);
+		com_edge[b].push_back(a);
+	}
+	bfs(1);
+	cout << coun;
+	return 0;
+}
+
+
+
+//* �ι�° Ǯ�� (union-find �̿�)
+#include<iostream>
+using namespace std;
+int parent [101];      //���ǻ���� �θ���ǻ�͸� �����ϴ� �迭
+int find_parent(int a) {      //��Ʈ ��ǻ�͸� ã�� �Լ�
+	if (a == parent[a]) return a;
+	else return parent[a] = find_parent(parent[a]);
+
+}
+void add(int a, int b) {    //�ΰ��� ��ǻ�Ͱ� ���� ������ ������ ��ġ�� �Լ�
+	a = find_parent(a);
+	b = find_parent(b);
+	if (a > b) parent[a] = b;
+	else parent[b] = a;
+}
+int main(void) {
+	ios_base::sync_with_stdio(false);
+	cin.tie(NULL);
+	int com_num, edge,a,b;       
+	cin >> com_num >> edge;
+	for (int i = 1; i <= com_num; i++) {   //����ó�� �ڽ��� �θ�� �ڽ��̱⿡ �ʱ�ȭ���ش�.
+		parent[i] = i;
+	}
+	for (int i = 0; i < edge; i++) {
+		cin >> a >> b;
+		add(a, b);
+	}
+	int coun = 0;
+	for (int i = 1; i <= com_num; i++) {     // ���ǻ���� ��Ʈ��ǻ�Ͱ� 1�̶�� 1�� ����� ���� �����̹Ƿ� ���ڸ� ī��Ʈ�Ѵ�.
+		if (find_parent(i) == 1) coun++;
+	}
+	
+	cout << coun-1;    //1�� ��ǻ�Ϳ����� ������ ��ǻ���� ���� ���°��̹Ƿ� 1����ǻ�͸� �������ش�.
+	return 0;
+}
+