stones = [int(i) for i in input().split()]

down = min(stones)
top = max(stones)

def binary_search(down, top):
    mid = (down + top) >> 1
    if mid == down:
        return mid
    lack = 0
    plus = 0
    for s in stones:
        if s <= mid:
            lack += mid - s
        else:
            plus += (s - mid) >> 1
    if lack <= plus:
        return binary_search(mid, top)
    else:
        return binary_search(down, mid)

print(binary_search(down, top))