Theatre Square in the capital city of Berland has a rectangular shape with the size n × m meters. On the occasion of the city’s anniversary, a decision was taken to pave the Square with square granite flagstones. Each flagstone is of the size a × a.
What is the least number of flagstones needed to pave the Square? It’s allowed to cover the surface larger than the Theatre Square, but the Square has to be covered. It’s not allowed to break the flagstones. The sides of flagstones should be parallel to the sides of the Square.
Input
The input contains three positive integer numbers in the first line: n, m and a (1 ≤ n, m, a ≤ 109).
Output
Write the needed number of flagstones.
拒绝分析：愚蠢的long long，干脆以后看到int就用long long算了
ac代码
#include <iostream>
#include <cmath>
#include <iomanip>
using namespace std;
int main()
{
long long n, m, a;
long long _n, _m;
cin >> n >> m >> a;
if (n%a == 0)
_n = n / a;
else _n = n / a + 1;
if (m%a == 0)
_m = m / a;
else _m = m / a + 1;
cout << _m * _n << endl;
}