import sys
input = sys.stdin.readline

N, X = map(int, input().split())
S = list(map(int, input().split()))
su = sum(S)

for Si in S:
    if Si%2==0:
        t = su-Si+Si//2
        
        if t%(N-1)==0 and t//(N-1)==X:
            print(Si//2)
            exit()