#include <stdio.h>
#include <stdlib.h>
#include <iostream>
#include <vector>
#include <string>
#include <queue>
#include <algorithm>
#include <math.h>
#include <utility>
#include <set>
#include <map>
#include <cstring>
#include <cstdio>
#include <stack>
#include <cmath>
#define INF 10000000000
#define MOD 10000000007
#define rep(i,n) for(int i =0;i<n;i++)
using namespace std;
typedef long long int ll;
typedef pair<int, int> i_i;


int main(){
    double a,b,x,y;
    cin >> a >> b >> x >> y;
    double ans ;
    if (x*b/a<=y) {
        ans = x + x*b/a;
    }else{
        ans = y + y*a/b;
    }
    printf("%.6lf\n",ans);
}