n, x = map(int, input().split())
s = list(map(int, input().split()))

fromLeft = [0] * (n + 1)
fromRight = [0] * (n + 1)

for i in range(len(s)):
    fromLeft[i + 1] = fromLeft[i] + s[i]

for i in reversed(range(len(s))):
    fromRight[i] = fromRight[i + 1] + s[i]

for i in range(len(s)):
    if s[i] % 2 != 0:
        continue
    half = s[i] // 2
    
    if fromLeft[i] + fromRight[i + 1] + half == (n - 1) * x:
        print(half)
        exit()