#pragma GCC optimize("Ofast,unroll-loops,O3") #include <bits/stdc++.h> using namespace std; #ifdef LOCAL #include "algo/debug.h" #else #define debug(...) 42 #endif using int64 = int64_t; using ld = long double; using uint64 = uint64_t; using int128 = __int128_t; #define all(v) (v).begin(), (v).end() #define rall(v) (v).rbegin(), (v).rend() const int md = 1e9 + 7; const int64 inf = 1e18; int main() { ios_base::sync_with_stdio(false); cin.tie(nullptr); cout.tie(nullptr); int n, cs, cf; cin >> n >> cs >> cf; vector<vector<vector<vector<int>>>> dp(n + 1, vector<vector<vector<int>>>(n + 1, vector<vector<int>>(n + 1, vector<int>(2, 0)))); vector<vector<vector<vector<int>>>> pref(n + 1, vector<vector<vector<int>>>(n + 1, vector<vector<int>>(n + 1, vector<int>(2, 0)))); dp[2][1][2][0] = 1; dp[2][2][1][1] = 1; for (int l = 2; l <= n; l++) { for (int s = 1; s <= l; s++) { for (int f = 1; f <= l; f++) { if (s != f && l > 2) { dp[l][s][f][0] = (dp[l][s][f][0] + pref[l - 1][l - 1][f - int(f > s)][1] - pref[l - 1][s - 1][f - int(f > s)][1] + md) % md; dp[l][s][f][1] = (dp[l][s][f][1] + pref[l - 1][s - 1][f - int(f > s)][0]) % md; } pref[l][s][f][0] = (pref[l][s - 1][f][0] + dp[l][s][f][0]) % md; pref[l][s][f][1] = (pref[l][s - 1][f][1] + dp[l][s][f][1]) % md; } } } cout << (dp[n][cs][cf][0] + dp[n][cs][cf][1]) % md << '\n'; return 0; }