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

public class Solution {
    
    static int fctrl(int n){    
        if (n == 0)    
            return 1;    
        else    
            return(n * fctrl(n-1));    
    }    

    static long countArray(int n, int k, int x) {
        long count = 0;
        if((n>=3) && (k>=2) && (x>=1)) {
            int newn = n-1;
            count = fctrl(n-2);
            return count+countArray(newn,k,x);
        } else {
            return count;
        }
    }

    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();
    }
}