#include <iostream>
#include <sstream>
#include <fstream>
#include <cstring>
#include <vector>
#include <deque>
#include <queue>
#include <stack>
#include <set>
#include <map>
#include <algorithm>
#include <functional>
#include <utility>
#include <bitset>
#include <cmath>
#include <cstdlib>
#include <ctime>
#include <cstdio>

using namespace std;

typedef long long ll;
typedef long double ld;
typedef pair<int, ll> P;
typedef pair<ll, P> Pl;

#define fr first
#define sc second
#define mp make_pair
#define pb push_back
#define rep(i,x) for(int i=0;i<x;i++)
#define rep1(i,x) for(int i=1;i<=x;i++)
#define rrep(i,x) for(int i=x-1;i>=0;i--)
#define rrep1(i,x) for(int i=x;i>0;i--)
#define sor(v) sort(v.begin(),v.end())
#define rev(s) reverse(s.begin(),s.end())
#define lb(vec,a) lower_bound(vec.begin(),vec.end())
#define ub(vec,a) upper_bound(vec.begin(),vec.end())
#define uniq(vec) vec.erace(unique(vec.begin(),vec.end(),vec.end))
#define mp1(a,b,c) P1(a,P(b,c))
#define all(x) (x).begin(),(x).end()

#define MAX 10000
#define NIL -1

struct Node { int p, l, r; };

static const int N = 100;

double a, b, x, y;

int main(){
	
	//scanf("%d%d%d%d", &a, &b, &x, &y);
	cin>>a>>b>>x>>y;
	if (y >= x*b/a){
		printf("%.10lf\n", x+x*b / a);
	}
	else{
		printf("%.10lf\n", y + y*a / b);
	}
	return 0;
}