#include <stdio.h>
int main(){
    int weight, speed;
    float balance, tilt;
    float stabilityIndex;
    
    scanf("%d", &weight);
    scanf("%d", &speed);
    scanf("%f", &balance);
    scanf("%f", &tilt);
    
    if (weight <= 0 || speed <= 0 || balance <= 0 || tilt <= 0){
        printf("Invaild inpput");
        return 0;
    }
    stabilityIndex = ((double)weight * (double)speed / (balance + tilt);
    printf("%.2f", stabilityIndex);
    
    return 0;
}