diff --git a/cpp/2304/230406.cpp b/cpp/2304/230406.cpp
new file mode 100644
index 0000000..eb2a7a3
--- /dev/null
+++ b/cpp/2304/230406.cpp
@@ -0,0 +1,60 @@
+#include <functional>
+#include <iostream>
+#include <queue>
+#include <utility>
+#include <vector>
+
+/**
+ * 1254. Number of Closed Islands
+ *
+ * Given a 2D grid consists of 0s (land) and 1s (water).  An island is a maximal 4-directionally connected group of 0s and a closed island is an island totally (all left, top, right, bottom) surrounded by 1s.
+ * Return the number of closed islands.
+ */
+
+class Solution {
+private:
+	static const inline int dX[] = {0, 1, 0, -1}, dY[] = {1, 0, -1, 0};
+public:
+	static int closedIsland(std::vector<std::vector<int>>&);
+};
+
+int Solution::closedIsland(std::vector<std::vector<int>>& G) {
+	const int m = G.size(), n = G.front().size();
+	auto setAs1 = [&](int x, int y) {
+		if (G[x][y]) return 0;
+		std::queue<std::pair<int, int>> q;
+		q.emplace(x, y);
+		for (int nx, ny; !q.empty(); q.pop()) {
+			auto&& [cx, cy] = q.front();
+			G[cx][cy] = 1;
+			for (int i = 0; i < 4; ++i) {
+				nx = cx + dX[i];
+				ny = cy + dY[i];
+				if (nx >= 0 && nx < m && ny >= 0 && ny < n && G[nx][ny] == 0)
+					q.emplace(nx, ny);
+			}
+		}
+		return 1;
+	};
+	for (int i = 0; i < n; ++i)
+		setAs1(0, i), setAs1(m - 1, i);
+	for (int i = 1; i < m; ++i)
+		setAs1(i, 0), setAs1(i, n - 1);
+	int ret = 0;
+	for (int i = 1; i < m - 1; ++i)
+		for (int j = 1; j < n - 1; ++j)
+			ret += setAs1(i, j);
+	return ret;
+}
+
+int main() {
+	std::vector<std::vector<int>> a {
+		{1,1,1,1,1,1,1,0},
+		{1,0,0,0,0,1,1,0},
+		{1,0,1,0,1,1,1,0},
+		{1,0,0,0,0,1,0,1},
+		{1,1,1,1,1,1,1,0}
+	};
+	std::cout << Solution::closedIsland(a);
+	return 0;
+}
diff --git a/cpp/2304/CMakeLists.txt b/cpp/2304/CMakeLists.txt
index bac0374..3d86cfd 100644
--- a/cpp/2304/CMakeLists.txt
+++ b/cpp/2304/CMakeLists.txt
@@ -4,4 +4,4 @@ PROJECT(2304)
 SET(CMAKE_CXX_STANDARD 23)
 SET(CMAKE_EXPORT_COMPILE_COMMANDS true)
 
-ADD_EXECUTABLE(2304 230406-CN.cpp)
+ADD_EXECUTABLE(2304 230406.cpp)