#!/bin/python3

import sys
import math
def countArray(n, k, x):
    # Return the number of ways to fill in the array.
    if k>= (n-2):
        if x<= k:
            return int((math.factorial(k)/math.factorial(k-n+2))-(k-1)-(k-2))
        else:
            return int((math.factorial(k)/math.factorial(k-n+2))-(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)