n, x = map(int, input().split())
s = list(map(int, input().split()))
t = sum(s)
for i in range(n):
  tmp = (t - s[i]//2) // (n-1)
  if tmp == x and s[i]%2 == 0 and (t - s[i]//2)%(n-1)==0:
    print(s[i] // 2)
    exit()