import java.util.*;

public class Hackerrank
{
    public static void main(String[] args)
    {
        Scanner in = new Scanner(System.in);
        int n = in.nextInt();
        int k = in.nextInt();
        int x = in.nextInt();
        double res = nCr(k,n-2);
        System.out.println((long)res);
    }

    static double nCr(int n, int r){
        int rfact=1, nfact=1, nrfact=1,temp1 = n-r ,temp2 = r;
        if(r>n-r)
        {
            temp1 =r;
            temp2 =n-r;
        }
        for(int i=1;i<=n;i++)
        {
            if(i<=temp2)
            {
                rfact *= i;
                nrfact *= i;
            }
            else if(i<=temp1)
            {
                nrfact *= i;
            }
            nfact *= i;
        }
        return nfact/(double)(rfact*nrfact);
    }
}