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
#include <bits/stdc++.h>
using namespace std;
#define DEBUG_MODE
#define endl '\n'
#ifdef DEBUG_MODE
#define DEBUG(X) debug_func(X, #X)
#define DEBUG_ENDL endl
#define DEBUG_SEPARATOR_LINE cout<<"=================\n"
#else
#define DEBUG(X) 0
#define DEBUG_ENDL 0
#define DEBUG_SEPARATOR_LINE 0
#endif
#define ALL(V) (V).begin(), (V).end()
#define ALLR(V) (V).rbegin(), (V).rend()
#define DEBUG_ENDL_S(S) ((S).size() ? "\n" : "")
template <typename T> using V = vector<T>;
template <typename T> using VV = V<V<T>>;
template <typename T, typename U> using P = pair<T, U>;
using ll = int64_t;
using PLL = P<ll, ll>;
template <typename T> const T& var_min(const T &t) { return t; }
template <typename T> const T& var_max(const T &t) { return t; }
template <typename Head, typename... Tail> const Head& var_min(const Head &head, const Tail&... tail) { return min(head, var_min(tail...)); }
template <typename Head, typename... Tail> const Head& var_max(const Head &head, const Tail&... tail) { return max(head, var_max(tail...)); }
template <typename T, typename... Tail> void chmin(T &t, const Tail&... tail) { t = var_min(t, tail...); }
template <typename T, typename... Tail> void chmax(T &t, const Tail&... tail) { t = var_max(t, tail...); }
void debug_func_preffix(const string &s) { if(s.size()) cout << s << " = "; }
template <typename T>
void debug_func(const T &t, const string &s = "") {
    debug_func_preffix(s);
    cout << t << DEBUG_ENDL_S(s);
}
template <typename T, typename U>
void debug_func(const P<T, U> &p, const string &s = "") {
    debug_func_preffix(s);
    cout << "(";
    debug_func(p.first);
    cout << ", ";
    debug_func(p.second);
    cout << ")" << DEBUG_ENDL_S(s);
}
template <typename T>
void debug_func(const V<T> &v, const string &s = "") {
    for(ll i = 0; i < v.size(); i++) {
        string t = s + "[" + to_string(i) + "]";
        debug_func(v[i], t);
    }
}

int main() {
    ll H, W, A, B;
    cin >> H >> W >> A >> B;
    cout << H * W - (H / A) * (W / B) * A * B << endl;
    return 0;
}

