#include<stdio.h>
int main()
{
	int a, b, x, y;
	scanf("%d %d %d %d", &a, &b, &x, &y);
	if (x * b < y * a)
		printf("%.20lf\n", (double)(a + b) * x / a);
	else
		printf("%.20lf\n", (double)(a + b) * y / b);
	return 0;
}