N,X = map(int,input().split())
S = list(map(int,input().split()))
sumA = X
A = []
for s in S:
    a = X - s
    A.append(a)
X = sum(A)
for i in range(N):
    if X-A[i] == S[i]//2:
        ans = S[i]//2
        break

print(ans)