#include<cstdio>
using namespace std;
typedef long long ll;
ll n,l,r;
ll f[30][30][30]={0};
int main(){
	freopen("pole.in","r",stdin);
	freopen("pole.out","w",stdout);
	scanf("%lld%lld%lld",&n,&l,&r);
	f[1][1][1]=1;
	for (int k=2;k<=n;k++){
		for (int i=1;i<=k;i++){
			for (int j=1;j<=k;j++)if (i+j-1<=k){
				f[i][j][k]=f[i-1][j][k-1]+f[i][j-1][k-1]+f[i][j][k-1]*(k-2);
				//printf("%d %d %d %d\n",k,i,j,f[i][j][k]);
			}
		}
	}
	printf("%lld",f[l][r][n]);
	return 0;
}