func_code_string: #include <bits/stdc++.h>   using namespace std;   const long long maxn = 4010;   const long long mod = 1e9 + 9;   long long f[maxn * 2][maxn], n, w, b;   long long num[maxn * 2], inv[maxn * 2];   long long pp(long long a, long long b) {     if (!b) return 1;     long long cnt = pp(a, b / 2);     cnt = 1ll * cnt * cnt % mod;     if (b & 1) cnt = 1ll * cnt * a % mod;     return cnt;   }   long long calc(long long n, long long m) {     if (n < m) return 0;     return 1ll * num[n] * num[n - 1] % mod * inv[m - 1] % mod * inv[n - m] % mod;   }   int main() {     cin >> n >> w >> b;     f[1][1] = 1;     for (long long i = 2; i <= w + b; ++i)       for (long long j = 1; j <= min(n, i); ++j)         f[i][j] = (1ll * f[i - 1][j] * j + f[i - 1][j - 1]) % mod;     num[0] = 1;     for (long long i = 1; i <= w + b; ++i) num[i] = 1ll * num[i - 1] * i % mod;     inv[w + b] = pp(num[w + b], mod - 2);     for (long long i = w + b - 1; i >= 0; --i)       inv[i] = 1ll * inv[i + 1] * (i + 1) % mod;     long long ans = 0;     for (long long i = 1; i < n - 1; ++i) {       long long cur = n - i - 1;       cur = 1ll * cur * calc(w, n - i) % mod * calc(b, i) % mod;       (ans += cur) %= mod;     }     cout << ans << endl;     return 0;   }   