N, X = map(int, input().split())
S = list(map(int, input().split()))
A = []
B = []
for i in range(N):
    A.append(X - S[i])
    B.append(X - (S[i] / 2))

sumA = sum(A)
for i in range(N):
    if B[i] + (sumA - A[i]) == X:
        ans = i
        break
    
print(S[ans] // 2)