#include "bits/stdc++.h" using namespace std; #define FOR(i,j,k) for(int (i)=(j);(i)<(int)(k);++(i)) #define rep(i,j) FOR(i,0,j) #define each(x,y) for(auto &(x):(y)) #define mp make_pair #define mt make_tuple #define all(x) (x).begin(),(x).end() #define debug(x) cout<<#x<<": "<<(x)< pii; typedef vector vi; typedef vector vll; int main(){ ios::sync_with_stdio(false); cin.tie(0); double x; while(cin >> x) { double ans = 0; for(int i = 1; i <= 10000000; ++i) { ans += 1.0 / ((x + i)*(x + i)); } cout << setprecision(20) << ans << endl; } }