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))