diff --git a/flydongwoo/AlgoLeadMe_Week20_prob01.cpp b/flydongwoo/AlgoLeadMe_Week20_prob01.cpp
new file mode 100644
index 0000000..f8d0a4c
--- /dev/null
+++ b/flydongwoo/AlgoLeadMe_Week20_prob01.cpp
@@ -0,0 +1,23 @@
+#include <algorithm>
+#include <iostream>
+#include <vector>
+using namespace std;
+int main(void) {
+	int n;
+	cin >> n;
+	vector<int>line;
+
+	for (int i = 0; i < n; i++) {
+		int k;
+		cin >> k;
+		line.push_back(k);
+	}
+	sort(line.begin(), line.end());
+
+	int answer = 0;
+	for (int i = 0; i < n; i++) {
+		answer += line[i] * (n - i);
+	}
+	cout << answer;
+
+}
\ No newline at end of file
diff --git a/flydongwoo/README.md b/flydongwoo/README.md
index da77089..3e5cafc 100644
--- a/flydongwoo/README.md
+++ b/flydongwoo/README.md
@@ -21,4 +21,5 @@
 | 17차시 | 2025.08.06 |  DFS와 BFS  | [바이러스](https://www.acmicpc.net/problem/2606)|https://github.com/AlgoLeadMe/AlgoLeadMe-15/pull/63|
 | 18차시 | 2025.08.07 |  BFS  | [숨바꼭질](https://www.acmicpc.net/problem/1697)|https://github.com/AlgoLeadMe/AlgoLeadMe-15/pull/64|
 | 19차시 | 2025.08.14 |  Sliding Window  | [수열](https://www.acmicpc.net/problem/2559)|https://github.com/AlgoLeadMe/AlgoLeadMe-15/pull/71|
+| 20차시 | 2025.08.27 |  Greedy Algorithm  | [ATM](https://www.acmicpc.net/problem/2559)|https://github.com/AlgoLeadMe/AlgoLeadMe-15/pull/81|