#include <cstdio>
#include <algorithm>
using namespace std;

int main(){
	int a,b,x,y;scanf("%d%d%d%d",&a,&b,&x,&y);
	double ans=min((double)x/a,(double)y/b);
	printf("%.7f\n",ans*a+ans*b);

	
	return 0;
}