func_code_string: #include <bits/stdc++.h>   using namespace std;   double calcC(int N, int M) {     if (M > N) return 0;     M = min(N - M, M);     double res = 1;     for (int i = 1; i <= M; ++i) res *= N - M + i, res /= i;     return res;   }   int main() {     int N, M;     while (cin >> N >> M) {       double result = 0;       for (int k = 1; k <= N; ++k) {         double tmp = 1;         tmp = calcC(M, k) * calcC(N * M - M, N - k) * k * k;         tmp /= calcC(N * M, N) * N * N;         result += tmp;       }       result *= N;       cout << setprecision(10) << result << endl;     }   }   