// #pragma GCC optimize("Ofast,unroll-loops")
// el psy congroo
#include <bits/stdc++.h>
using namespace std;
#define int long long int
#define ins insert
#define pii pair<int,int>
#define pb push_back
#define endl '\n'
#define putr(x) cout<<x<<endl;return;
#define all(x) x.begin(),x.end()
const int mod = 1e9 +7, sze = 2e3+23, inf = 2e9, LG = 19,pr = 31;
int dp[sze][sze];
void fast(){
int n,a,b;
cin>>n>>a>>b;
dp[1][1]=1;
for(int i =2;i<=n;i++){
for(int j=1;j<=i;j++){
// i,j
if( i==a || i==b ){
dp[i][j] = dp[i-1][j-1]+ dp[i-1][j];
}
else{
// cout<<i<<" "<<j<<" :"<<dp[i-1][j]<<" "<<dp[i-1][j+1]<<" "<<dp[i-1][j+1]*(j+1 - (i>a) - (i>b))<<endl;
dp[i][j] = (dp[i-1][j+1] + dp[i-1][j-1]*(j+1 - (i>a) - (i>b)));
}
// cout<<i<<" "<<j<<" "<<dp[i][j]<<endl;
}
}
putr(dp[n][1]);
}
signed main(){
ios::sync_with_stdio(0);
cin.tie(0);
cout.tie(0);
int tt = 1;
// cin>>tt;
while(tt--){
fast();
}
return 0;
}
