import sys

sys.setrecursionlimit(10 ** 7)
input = sys.stdin.readline
f_inf = float('inf')
mod = 10 ** 9 + 7


def resolve():
    n, x = map(int, input().split())
    S = list(map(int, input().split()))

    tot = sum(S)
    for i in range(n):
        if S[i] % 2 == 0:
            if tot - S[i] // 2 == x * (n - 1):
                print(S[i] // 2)
                break


if __name__ == '__main__':
    resolve()