#include<stdio.h>
 struct student{
     int score;
     
 };
 int main()
 {
     int size,ind;
     float sum=0.0,avg;
     scanf("%d",&size);
     if(size<0)
     {
         printf("Invalid input");
         return 0;
     if(!scanf("%d",&size)==1)
     {
         printf("Invalid input");     }
 }
 struct student stud[ind];
 for(ind=0;ind<size;ind++){
     if(scanf("%d",&stud[i].score)!=1 || stud[i].score<0){
         printf("Invalid input");
         return 0;
     }
     sum+=stud[ind].score;
 }
 avg=sum/size;
 printf("%.2f",avg);
 return 0;
 }