#include <fstream>
#include <algorithm>
#define N 23
using namespace std;
typedef long long ll;
ifstream in("pole.in");
ofstream out("pole.out");
int n,l,r;
ll f[N][N][N]={0};
void read()
{
	in>>n>>l>>r;
}
void work()
{
	int i,j,k;
	f[n][1][1]=1;
	for(i=n-1;i>=1;i--)
	{
		for(j=1;j<=l;j++)
		{
			for(k=1;k<=r;k++)
			{
				f[i][j][k]=f[i+1][j-1][k]+f[i+1][j][k-1]+f[i+1][j][k]*(n-i-1);
			}
		}
	}
	out<<f[1][l][r]<<endl;
}
int main()
{
	read();
	work();
	return 0;
}