//In The Name Of ALLAH! #pragma GCC optimize("O3") #include <bits/stdc++.h> #include <ext/pb_ds/assoc_container.hpp> #include <ext/pb_ds/tree_policy.hpp> using namespace __gnu_pbds; using namespace std; #define ll long long #define ld long double #define endl '\n' #define pb push_back #define pf push_front #define Zemur007 ios_base::sync_with_stdio(false); cin.tie(NULL); cout.tie(NULL); #define bpc __builtin_popcountll #define btz __builtin_ctzll #define all(x) x.begin() , x.end() #define allr(x) x.rbegin() , x.rend() #define F first #define S second #define pll pair<ll , ll> #define turtle tuple<ll , ll , ll> #define pss pair<string , string> #define YES cout << "YES" << endl; #define NO cout << "NO" << endl; #define indexed_set tree<pll , null_type , less<pll> , rb_tree_tag , tree_order_statistics_node_update> const ll sz = 2e3 + 5 , INF = 1e18 , MOD = 1e9 + 7; ll dp[sz][sz]; //dp[i][j] ilk i ədəd istifadə etsək şərtə uyğun j dənə ayrı component yaransa yolların sayı ll mul(ll a , ll b){ return ((a % MOD) * (b % MOD)) % MOD; } ll mask , i , j , l , k; void solve(){ ll n , cs , cf; cin >> n >> cs >> cf; dp[1][1] = 1; ll used = 0; for(i = 2 ; i <= n ; i++){ used += (i == cs || i == cf); for(j = 1 ; j <= i ; j++){ if(i == cs || i == cf){ dp[i][j + 1] = (dp[i][j + 1] + dp[i - 1][j]) % MOD; dp[i][j] = (dp[i][j] + dp[i - 1][j]) % MOD; } else{ if(j + 1 <= i) dp[i][j + 1] = (dp[i][j + 1] + mul(dp[i - 1][j] , j + 1 - used)); dp[i][j - 1] = (dp[i][j - 1] + mul(dp[i - 1][j] , j - 1)) % MOD; } } } cout << dp[n][1] << endl; } signed main(){ Zemur007; //open; ll t = 1; // cin >> t; while(t--){ solve(); } // for(ll testcase = 1 ; testcase <= t ; testcase++){ // cout << "Case " << testcase << ":" << endl; // solve(); // } }