#include <bits/stdc++.h> using namespace std; typedef long long int64; const int maxn = 2e3 + 2; const int64 mod = 1e9 + 7; int64 dp[maxn][maxn]; int main() { int n,a,b; cin >> n >> a >> b; dp[0][0] = 1; for (int64 i = 1; i <= n; i++){ for (int64 j = 1; j <= i; j++){ if (i == a || i == b) { dp[i][j] = (dp[i-1][j-1] + dp[i-1][j]) % mod; } else { dp[i][j] = (dp[i-1][j + 1] * j % mod + dp[i-1][j-1] * (j - (i > a) - (i > b)) % mod) % mod; } } } cout << dp[n][1]; return 0; }