n,k = map(int,input().split())
ns=list(map(int,input().split()))
cnt=0
for i in ns:
    cnt += k-i
    
for i in range(n):
    if ns[i]%2 != 0:
        continue
    t=k-ns[i]
    t2=k-(ns[i]//2)
    if (cnt-t) + t2 == k:
        print(ns[i]//2)
        break