x, y, r = map(int, raw_input().split())
x, y = abs(x), abs(y)

low, high = 0, 10 ** 9
while high - low > 1:
	mid = (low + high) / 2
	if (x + y - mid) ** 2 > 2 * r ** 2 and x + y < mid:
		high = mid
	else:
		low = mid

print high