#include <iostream>
using namespace std;
int main(){
int n = 15;
if (n < 3 || n%3 != 0){
return 0;
}
int k = n / 3;
double res = 0;
for (int i=1; i<=k; i++){
res += 1.0/(i*3);
cout << res;
#include <iostream>
using namespace std;
int main(){
int n = 15;
if (n < 3 || n%3 != 0){
return 0;
}
int k = n / 3;
double res = 0;
for (int i=1; i<=k; i++){
res += 1.0/(i*3);
}
cout << res;
return 0;
}