#include <bits/stdc++.h> #define ll long long #define int ll #define ld long double #define all(v) v.begin(),v.end() #define rall(v) v.rbegin(),v.rend() #define vi vector<int> #define vvi vector<vi> #define vvv vector<vvi> #define vpi vector<pair<int,int>> #define sz(v) (int)v.size() #define pb push_back #define ii pair<int,int> #define F first #define S second using namespace std; const int mod = 1e9+7, N = 100+5 ,M=1005; const ll inf = 1e18; int dx[] = {0, 0, 1, -1, 1, 1, -1, -1}; int dy[] = {-1, 1, 0, 0, 1, -1, 1, -1}; int n,s,e; vvi dp; int calc(int i,int c){ if(i>n) return c==1; int &ret=dp[i][c]; if(~ret) return ret; ret=0; if(i==s||i==e){ // new comp ret+=calc(i+1,c+1)%mod; // extend comp if(c) ret+=calc(i+1,c)%mod; ret%=mod; } else{ // new comp ret+=(c+1-(i>s)-(i>e))* calc(i+1,c+1)%mod; // combine 2 if(c>=2) ret+=(c-1)* calc(i+1,c-1)%mod; ret%=mod; } return ret; } void here_we_go_again() { cin>>n>>s>>e; dp.assign(n+5,vi(n+5,-1)); cout<<calc(1,0); } int32_t main() { ios_base::sync_with_stdio(false); cin.tie(0), cout.tie(0); int tc = 1; // cin >> tc; for(int i=1;i<=tc;++i) { // cout<<"Case #"<<i<<": "; here_we_go_again(); } return 0; }