#include <bits/stdc++.h>
#define FOR(i,a,b) for(int i=(a);i<(b);i++)
#define REP(i,b) FOR(i,0,b)
#define F first 
#define S second
#define PB push_back
#define BE(c) c.begin(),c.end()
using namespace std;
typedef long long LL;

typedef long double ut;
typedef vector<ut> VI;
const ut INF=1<<30;
const int SIZE=1<<12;
const ut eps=1e-9;

int main(){
	double A,B,X,Y;
	cin >>A >>B >> X >> Y;
	printf("%lf\n",min(A*Y,B*X)*(A+B)/(A*B));

	return 0;
}