diff --git a/xxubin04/README.md b/xxubin04/README.md
index c17d154..b30d0f6 100644
--- a/xxubin04/README.md
+++ b/xxubin04/README.md
@@ -56,4 +56,6 @@
 | 52차시 | 2024.07.05 |  구현  | <a href="https://school.programmers.co.kr/learn/courses/30/lessons/64065">[2019 카카오 인턴십]튜플 </a>  | https://github.com/AlgoLeadMe/AlgoLeadMe-3/pull/198 |
 | 53차시 | 2024.07.08 |  DP  | <a href="https://www.acmicpc.net/problem/2193">[2193]이친수 </a>  | https://github.com/AlgoLeadMe/AlgoLeadMe-3/pull/200 |
 | 54차시 | 2024.07.11 |  Tree  | <a href="https://www.acmicpc.net/problem/1991">[1991]트리 순회 </a>  | https://github.com/AlgoLeadMe/AlgoLeadMe-3/pull/203 |
-| 55차시 | 2024.07.29 |  정렬  | <a href="https://school.programmers.co.kr/learn/courses/30/lessons/42747?language=python3">[Programmers]H-Index </a>  | https://github.com/AlgoLeadMe/AlgoLeadMe-3/pull/208 |
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+| 55차시 | 2024.07.29 |  정렬  | <a href="https://school.programmers.co.kr/learn/courses/30/lessons/42747?language=python3">[Programmers]H-Index </a>  | https://github.com/AlgoLeadMe/AlgoLeadMe-3/pull/208 |
+| 56차시 | 2024.08.05 |  구현  | <a href="https://school.programmers.co.kr/learn/courses/30/lessons/17677#">[2018 KAKAO BLIND]뉴스 클러스터링 </a>  | https://github.com/AlgoLeadMe/AlgoLeadMe-3/pull/211 |
+| 57차시 | 2024.08.08 |  Hash  | <a href="https://school.programmers.co.kr/learn/courses/30/lessons/42888">[2019 KAKAO BLIND]오픈채팅방 </a>  | https://github.com/AlgoLeadMe/AlgoLeadMe-3/pull/215 |
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diff --git "a/xxubin04/\355\225\264\354\213\234\353\247\265/\354\230\244\355\224\210\354\261\204\355\214\205\353\260\251.py" "b/xxubin04/\355\225\264\354\213\234\353\247\265/\354\230\244\355\224\210\354\261\204\355\214\205\353\260\251.py"
new file mode 100644
index 0000000..3d91678
--- /dev/null
+++ "b/xxubin04/\355\225\264\354\213\234\353\247\265/\354\230\244\355\224\210\354\261\204\355\214\205\353\260\251.py"
@@ -0,0 +1,41 @@
+def msg(act, name):
+    if act == "Enter":
+        return name+"님이 들어왔습니다."
+    else:  # act == "Leave"
+        return name+"님이 나갔습니다."
+
+
+def solution(record):
+    answer = []
+    users = {}
+
+    for r in record:
+        splitRecord = r.split()
+        command = splitRecord[0]
+        userId = splitRecord[1]
+
+        if command == "Leave":
+            if userId in users:
+                users[userId].append((command, ""))
+            else:
+                users[userId] = [(command, "")]
+        else:
+            if userId in users:
+                users[userId].append((command, splitRecord[2]))
+            else:
+                users[userId] = [(command, splitRecord[2])]
+
+    nicknames = {}
+
+    for userId, action in users.items():
+        for command, name in reversed(action):
+            if command == "Enter" or command == "Change":
+                nicknames[userId] = name
+                break
+
+    for output in record:
+        splitOutput = output.split()
+        if splitOutput[0] != "Change":
+            answer.append(msg(splitOutput[0], nicknames[splitOutput[1]]))
+
+    return answer
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