#include<stdio.h>//#include<bits/stdc++.h>#include<string.h>#include<iostream>#include<math.h>#include<sstream>#include<set>#include<queue>#include<map>#include<vector>#include<algorithm>#include<limits.h>#define MAXN (100000+10)#define MAXM (100000)#define inf 0x3fffffff#define INF 0x3f3f3f3f#define lson l,m,rt<<1#define rson m+1,r,rt<<1|1#define LL long long#define ULL unsigned long longusing namespace std;double a[1000000];void cmd(){    a[0]=0;    a[1]=1;    for(long long i=2; i<1000000; i++)    {        a[i]=a[i-1]+1.0/(i*i);    }}int main(){    string s;    cmd();    while(cin>>s)    {        if(s.length()>=7)        {            printf("%.5f\n",a[1000000-1]);        }        else        {            int b=0;            for(int i=0; i<s.length(); i++)            {                b=b*10+s[i]-‘0‘;            }            printf("%.5f\n",a[b]);        }    }    return 0;}