import java.io.*;
import java.util.*;
import java.text.*;
import java.math.*;
import java.util.regex.*;

public class Solution {

    static long countArray(int n, int k, int x) {
        // Return the number of ways to fill in the array.
        int ncr=nCr(n,x);
        long result=(long)(ncr/(n-2));
        return result;
    }
    
    static int nCr(int n,int r){
        int[] C=new int[r+1];
        C[0]=1;
        for(int i=1;i<=n;i++){
         for(int j=(int)Math.min(i,r);j>0;j--)
            C[j]=C[j]+C[j-1];
    }
    return C[r];
    }
    
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        int n = in.nextInt();
        int k = in.nextInt();
        int x = in.nextInt();
        long answer = countArray(n, k, x);
        System.out.println(answer);
        in.close();
    }
}