func_code_string: #include <bits/stdc++.h>   using namespace std;   int N, M;   long double DP[1010][1010];   int i, j;   int total, X;   int main() {     cin >> N >> M;     DP[0][0] = 1.0;     for (int i = 1; i <= N; i++)       for (int j = 0; j <= M && j <= N; j++) {         total = N * M - (i - 1);         X = M - j;         DP[i][j] += DP[i - 1][j] * (1.0 * total - X) / (1.0 * total);         if (j > 0) {           total = N * M - (i - 1);           X = M - j + 1;           DP[i][j] += DP[i - 1][j - 1] * (1.0 * X) / (1.0 * total);         }       }     long double ans = 0;     for (int i = 1; i <= N; i++)       ans += (1.0 * i) * (1.0 * i) / (1.0 * N) * DP[N][i];     cout << fixed << setprecision(20) << ans <<   n ;     return 0;   }   