#include <stdio.h>
int main(){
int n;
double v;
double sum=0.0,avg=0.0;
if (scanf("%d",&n)!=EOF){
for (int i=0;i<n;i++){
if (scanf("%lf",&v)!=EOF){
sum+=1.0/v;
}
}
avg = 1.0*n/sum;
printf("%.2lf",avg);
}
return 0;
}
京公网安备 11010702002337 号