#include <stdio.h>

int main(void){
    int i, a, b, x, y;
    scanf("%d %d %d %d", &a, &b, &x, &y);
    double coffee = (double)x/a, tea = (double)y/b;
    if(coffee<=tea){
        tea = coffee * b;
        printf("%.7lf\n", x + tea);
    }else{
        coffee = tea * a;
        printf("%.7lf\n", coffee + y);
    }
    return 0;
}