//Author RufatM #pragma GCC optimize("Ofast") #include <bits/stdc++.h> #include <ext/pb_ds/assoc_container.hpp> #include <ext/pb_ds/tree_policy.hpp> #include <ext/pb_ds/detail/standard_policies.hpp> using namespace __gnu_pbds; using namespace std; typedef long long ll; typedef pair<int,int> pii; typedef pair<ll,ll> pll; typedef vector<int> vi; typedef vector<vector<int>> vvi; typedef vector<ll> vll; typedef vector<bool> vb; typedef vector<string> vs; #define fastio ios_base::sync_with_stdio(false);cin.tie(0);cout.tie(0); #define endl '\n' #define pb push_back #define pf push_front #define eb emplace_back #define ff first #define ss second #define all(x) begin(x),end(x) #define rall(x) rbegin(x),rend(x) #define mt19937_64 mt_rand(chrono::steady_clock::now().time_since_epoch().count()) #define ordered_set tree<int,null_type,less<int>,rb_tree_tag,tree_order_statistics_node_update> const int MOD=1000000007; const int INF=1000000007; const ll LINF=4e18; const int MAXN=2005; int n,s,l; ll dp[MAXN][MAXN][3]; void modpow(ll &a,ll b){ a+=b; if(a>=MOD){ a-=MOD; } if(a<0){ a+=MOD; } } signed main(){ fastio; #ifndef ONLINE_JUDGE //freopen("input.txt","r",stdin); //freopen("output.txt","w",stdout); #endif int t=1; //cin >> t; while(t--){ cin >> n >> s >> l; if(s==1 or l==1){ dp[1][1][1] = 1; } else{ dp[1][1][0] = 1; } for(int i=2;i<=n;i++){ for(int j=1;j<i;j++){ if(i==s or i==l){ for(int k=0;k<2;k++){ modpow(dp[i][j+1][k+1],dp[i-1][j][k]); modpow(dp[i][j][k+1],dp[i-1][j][k]); } } else{ for(int k=0;k<3;k++){ modpow(dp[i][j+1][k],(dp[i-1][j][k]*(j+1-k))%MOD); modpow(dp[i][j-1][k],(dp[i-1][j][k]*(j-1))%MOD); } } } } cout << dp[n][1][2] % MOD << endl; } }