报错信息：

Wrong Answer.wrong answer 1st numbers differ - expected: '1000000000000000000', found: '-1486618624'

源代码：

#include <bits/stdc++.h>
using namespace std;
int main() {
	long n, m, a, length, width;
	scanf("%d %d %d", &n, &m, &a);
	if (n % a > 0) length = n / a + 1;
	else length = n / a;
	if (m % a > 0) width = m / a + 1;
	else width = m / a;
	printf("%d",length*width);
	return 0;
}