// editor5
#include<stdio.h>
int main() {
    int weight, speed;
    float balance, tilt, stability_index;
    
    scanf("%d", &weight);
    scanf("%d", &speed);
    scanf("%f", &balance);
    scanf("%f", &tilt);
    
    if (weight <=0 || speed <=0 || balance <=0 || tilt <=0){
        printf("Invalid input\n");
    
    }else{
        stability_index = (float) / (weight + speed) / (balance + tilt);
        printf("%.2f\n", stability_index);
    }
    return 0;
}