#!/usr/bin/env python3
import sys

def main():
    # N = int(input())
    N, X = map(int,input().split())
    S = list(map(int,input().split()))
    all = sum(S)
    for i in S:
        if (all - i // 2) == X * (N - 1):
            print(i // 2)
            return
    return

if __name__ == '__main__':
    main()