#include <stdio.h>

int main(void) {
	int a, b, x, y;
	double x1, y1, x2, y2;
	double mix;
	scanf("%d%d%d%d", &a, &b, &x, &y);
	y1 = (double)b / a * x;
	x1 = (double)a / b * y;
	if(y >= y1){
		mix = x + y1;
	}
	else if(x >= x1){
		mix = x1 + y;
	}
	printf("%f\n", mix);

    return 0;
}