/* Telebe of Adicto && Mamedov yani AzeTurk810 I see humans but no humanity */ #include <iostream> #include <vector> //mt19937 rng(chrono::steady_clock::now().time_since_epoch().count()); using ll = long long; using namespace std; #define ln '\n' #define INFi 1e9 #define INFll 1e18 #define int ll constexpr int MOD = 1e9 + 7; void solve() { int n , cs , cf; cin >> n >> cs >> cf; vector< vector< int > > dp(n + 1 , vector< int > (n + 1,0)); dp[1][1] = 1; int say = 0; for(int i = 1;i <= n;i++) { if(i == cs || i == cf) say++; for(int j = 1;j < i;j++) { if(i == cs || i == cf) { dp[i][j + 1] += dp[i - 1][j]; dp[i][j] += dp[i - 1][j]; dp[i][j + 1] %= MOD; } else { dp[i][j + 1] += (j + 1 - say) * dp[i - 1][j]; dp[i][j - 1] += dp[i - 1][j] * (j - 1); dp[i][j - 1] %= MOD; dp[i][j + 1] %= MOD; } dp[i][j] %= MOD; } } cout << dp[n][1] << ln; } // Attack on titan<3 signed main() { ios::sync_with_stdio(0); cin.tie(nullptr); int t = 1; // cin >> t; for(int cases = 0 ; cases < t;cases ++) { solve(); } } // Just Imaginary