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

def solve(m): # m 個作れるか？
    res = 0
    for s in stones:
        if s > m:
            res += (s - m)//2
        
        elif s < m:
            res -= m - s
    return res >= 0

ok = 0
ng = 10**10
while abs(ok - ng) != 1:
    mid = (ok + ng)//2
    if solve(mid):
        ok = mid
    else:
        ng = mid
print(ok)