#include <stdio.h>
int main(){
    int weight, speed;
    float balance, tilt, stabilty_index;
    
    scanf("%d", &weight);
    scanf("%d", &speed);
    scanf("%f", &balance);
    scanf("%f", &tilt);
    
    if (weight <=0 || speed <=0 || balance <=0 || tilt <=0){
        printf("inavlid imput\n");
        
    }else{
        stabilty_index = (float)(weight * speed) / (balance + tilt);
        printf("%.2f"\n", stabilty_index);
    }
    return 0;
}