n, x = map(int, input().split())
s = list(map(int, input().split()))
sm = sum(s)
a = []
for ss in s:
    a.append(x-ss)
s = set(s)
b = []
sa = sum(a)
for aa in a:
    b.append(sa-aa)

for bb in b:
    if bb*2 in s:
        print(bb)
        exit(0)