#pragma GCC optimize("O3") #pragma GCC optimize ("unroll-loops") // #pragma GCC target("avx2") #include <bits/stdc++.h> #define ll long long #define ull unsigned ll #define ld long double #define all(v, l) v.begin() + l, v.end() #define rall(v, l) v.rbegin(), v.rend() - l #define pb push_back #define pf push_front #define rsz resize #define fi first #define se second #define LMAX LLONG_MAX #define LMIN LLONG_MIN #define IMAX INT_MAX #define IMIN INT_MIN #define endl "\n" #define newline cout << endl; using namespace std; const int MOD = 1000000007; // structs // globals // variables int n, s, e, ans; // iterators int i; // notes /* -stuff you should look for- * int overflow, array bounds * special cases (n=1?) * do something instead of nothing and stay organized * WRITE STUFF DOWN * DON'T GET STUCK ON ONE APPROACH continue - skip the rest in the loop */ // functions ll GCD(ll numeroune, ll numerodeux); ll LCM(ll numeroune, ll numerodeux); ll power(ll numeroune, ll numerodeux); void solve() { cin >> n >> s >> e; ans = 0; vector <bool> used(n + 1, false); used[s] = true; function <void(int, int, int)> f = [&](int eaten, int v, int par) { used[v] = true; eaten++; if (eaten == n) { if (v == e) { ans++; ans %= MOD; } return; } if (par < v) { for (int u = 1; u < v; u++) { if (used[u]) { continue; } f(eaten, u, v); } } else { for (int u = v + 1; u <= n; u++) { if (used[u]) { continue; } f(eaten, u, v); } } used[v] = false; }; for (i = s + 1; i <= n; i++) { f(1, i, s); } for (i = 1; i < s; i++) { f(1, i, s); } cout << ans; } int main() { ios_base::sync_with_stdio(0); cin.tie(0); int t = 1; // cin >> t; while (t--) { solve(); newline } } ll GCD(ll numeroune, ll numerodeux) { if (!numeroune) { return numerodeux; } return GCD(numerodeux % numeroune, numeroune); } ll LCM(ll numeroune, ll numerodeux) { return numeroune * numerodeux / GCD(numeroune, numerodeux); } ll power(ll numeroune, ll numerodeux) { ll res = 1; while (numerodeux) { if (numerodeux & 1) { res *= numeroune; } numeroune *= numeroune; numerodeux >>= 1; } return res; } /* $$$$$$$$\ $$$$$$$$\ $$ _____|\____$$ | $$ | $$ / $$$$$\ $$ / $$ __| $$ / $$ | $$ / $$$$$$$$\ $$$$$$$$\ \________|\________| */