題目：

Description
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?≤?10的9次方
).
Output
Write the needed number of flagstones.
Sample Input
Input
6 6 4
Output
4

這道題的意思是用aa的磚去鋪nm的地面，至少需要多少塊磚（磚不能切割）（覆蓋問題）？

這道題是一道很簡單的模擬數(shù)學(xué)題，但是當(dāng)時(shí)我想了好半天。

參考代碼：

#include <iostream>
#include <algorithm>
#include <cstring>
using namespace std;
typedef long long ll;

ll result(ll n, ll m, ll a) {
    ll ans = 0;
    ll a1 = n / a;
    if (n % a) a1 += 1;
    ll b1 = m / a;
    if (m % a) b1 += 1;
    return a1 * b1;
}

int main() {
    ios::sync_with_stdio(false);
    cin.tie(NULL);
    ll n, m, a;
    while (cin >> n >> m >> a) {
        ll ans = result(n, m, a);
        cout << ans << endl;
    }
    return 0;
}