from math import factorial

import sys

def countArray(n, k, x):
    return int(factorial(k) / factorial(k - n + 2))//2

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)