#!/bin/python3

import sys, math

def countArray(n, k, x):
    answer = math.factorial(k) // math.factorial(k - x) - (k - 1 + k - 2)
    return(answer)

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)