#!/bin/python3

import sys
import math

def nCr(n,r):
    f = math.factorial
    return f(n) // f(r) // f(n-r)

def countArray(n, k, x):
    return (nCr(n,k))-1

if __name__ == "__main__":
    n, k, x = input().strip().split(' ')
    n, k, x = [int(n), int(k), int(x)]
    answer = countArray(n, k, x)
    print(answer)