#include <stdio.h>

int main(){
    int weigth, 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("Invalid input");
    } else {
        
        stabilityIndex = (weight / speed) + (balance / tilt);
        printf("%.2f", stabilityIndex);
    }
    return 0;
    
}