L = list(map(int, input().split()))

def is_ok(x):
    p = 0
    q = 0
    for l in L:
        if l >= x:
            p +=(l-x)//2
        else:
            q += x-l
    if p >= q:
        return True
    else:
        return False

ok = 0
ng = 10**18
while ok+1 < ng:
    c = (ok+ng)//2
    if is_ok(c):
        ok = c
    else:
        ng = c
print(ok)