#include <stdio.h>

int main(){
    int weight, speed;
    float balance,tilt, stablity_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");
       return 0;
   }
   else{
   stability_index (float)(weight+speed)/(balance+tilt);
   printf("%.2f\n",stability_index);
   }
   return 0;
}