import java.util.*;
import java.lang.*;
import java.io.*;
class Ideone
{
public static void main
(String[] args
) { double x = 0;
Scanner in
=new Scanner
(System.
in); int n = in.nextInt();
for(int i = 1; i <= n; i++) {
x +=1/(i*i*i);
}
}
}
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