diff --git a/g0rnn/README.md b/g0rnn/README.md
index 584ca25..9529a76 100644
--- a/g0rnn/README.md
+++ b/g0rnn/README.md
@@ -31,4 +31,6 @@
 | 27차시 | 2025.06.15 | Floyd-Warshall | [케빈 베이컨의 6단계 법칙](https://www.acmicpc.net/problem/1389) | https://github.com/AlgoLeadMe/AlgoLeadMe-12/pull/113 |
 | 28차시 | 2025.06.27 | BFS | [상어 중학교](https://www.acmicpc.net/problem/21609) | https://github.com/AlgoLeadMe/AlgoLeadMe-12/pull/115 |
 | 29차시 | 2025.07.22 | combination | [소문난 칠공주](https://www.acmicpc.net/problem/1941) | https://github.com/AlgoLeadMe/AlgoLeadMe-12/pull/119 |
+| 30차시 | 2025.07.28 | segment-tree | [커피숍2](https://www.acmicpc.net/problem/1275) | https://github.com/AlgoLeadMe/AlgoLeadMe-12/pull/121 |
+
 ---
diff --git a/g0rnn/segment-tree/30-g0rnn.py b/g0rnn/segment-tree/30-g0rnn.py
new file mode 100644
index 0000000..3a3a906
--- /dev/null
+++ b/g0rnn/segment-tree/30-g0rnn.py
@@ -0,0 +1,45 @@
+import sys
+input = sys.stdin.readline
+
+def init(node, start, end):
+    if start == end:
+        tree[node] = nums[start]
+    else:
+        mid = (start + end) // 2
+        init(node * 2, start, mid)
+        init(node * 2 + 1, mid + 1, end)
+        tree[node] = tree[node * 2] + tree[node * 2 + 1]
+
+def update(node, start, end, idx, val):
+    if start == end:
+        nums[idx] = val
+        tree[node] = val
+    else:
+        mid = (start + end) // 2
+        if start <= idx <= mid:
+            update(node * 2, start, mid, idx, val)
+        else:
+            update(node * 2 + 1, mid + 1, end, idx, val)
+        tree[node] = tree[node * 2] + tree[node * 2 + 1]
+
+def query(node, start, end, l, r):
+    if r < start or end < l:
+        return 0
+    if l <= start and end <= r:
+        return tree[node]
+    mid = (start + end) // 2
+    return query(node * 2, start, mid, l, r) + query(node * 2 + 1, mid + 1, end, l, r)
+
+# 입력
+n, q = map(int, input().split())
+nums = [0] + list(map(int, input().split())) ## int는 가변 정수라 long 보다도 커질 수 있음.. 아니 걍 크기제한이 없음
+tree = [0] * (4 * n)
+
+init(1, 1, n)
+for _ in range(q):
+    x, y, a, b = map(int, input().split())
+    l = min(x, y)
+    r = max(x, y)
+    
+    print(query(1, 1, n, l, r))
+    update(1, 1, n, a, b)
\ No newline at end of file