#include<iostream>
#include<string>
#include<algorithm>
#include<functional>
#include<vector>
#include<set>
#include<queue>
#include<list>
#include<stdio.h>
#include<stdlib.h>
#include<map>
#include<cstdio>

#define rep(i,a,b) for(int i=a;i<b;i++)
#define rrep(i,a,b) for(int i=a;i>=b;i--)
#define fore(i,a) for(auto &i:a)
#define all(x) (x).begin(),(x).end()

typedef long long ll;

using namespace std;



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);
	}

	cout << ans << endl;
}