problem

I want to put as many rectangular tiles as possible on a rectangular wall with a size of $ h $ in height and $ w $ in width, and a size of $ a $ in height and $ b $ in width.

The following conditions must be met when attaching tiles.


* Do not stack tiles.
* Do not apply tiles diagonally, that is, any edge of the tile is parallel or perpendicular to any edge of the wall.
* Do not change the orientation of the tiles, that is, do not swap the vertical and horizontal directions.



When as many tiles as possible are pasted, find the sum of the areas not covered by the tiles.



output

Output the total area of ​​the part not covered by the tile. Also, output a line break at the end.

Example

Input

5 8
2 2


Output

8
#define _CRT_SECURE_NO_WARNINGS
#define _SILENCE_ALL_CXX17_DEPRECATION_WARNINGS
#include <stdio.h>
#include <algorithm>
#include <utility>
#include <functional>
#include <cstring>
#include <queue>
#include <stack>
#include <math.h>
#include <iterator>
#include <vector>
#include <string>
#include <set>
#include <math.h>
#include <iostream>
#include <random>
#include <map>
#include <fstream>
#include <iomanip>
#include <time.h>
#include <stdlib.h>
#include <list>
#include <typeinfo>
#include <list>
#include <set>
#include <assert.h>
#include <complex>
using namespace std;
#define eps 0.000001
#define LONG_INF 10000000000000
#define GOLD 1.61803398874989484820458
#define MAX_MOD 1000000007
#define MOD 998244353
#define seg_size 65536*4
#define REP(i,n) for(long long i = 0;i < n;++i)
int main() {
	int h, w, a, b;
	cin >> h >> w >> a >> b;
	cout << h * w - (h / a) * (w / b) * a* b << endl;
	return 0;
}
