s = list(map(int, input().split()))
def check(mid):
    total = 0
    excess=0
    lack=0
    for i in s:
        if i>=mid:
            excess=0
            lack =0
            excess = (i-mid)//2
        if i<mid:
            excess=0
            lack=0
            lack = i-mid
        total = total+excess+lack
    return total>=0

left = min(s)
right = max(s)
while True:
    mid = (left+right)//2
    if check(mid)==True:
        left = mid
    else:
        right = mid
    if right==mid+1:
        break
print(mid)