#define _CRT_SECURE_NO_WARNINGS
#include<sstream>
#include<iostream>
#include<cstdio>
#include<cstdlib>
#include<cstring>
#include<climits>
#include<cmath>
#include<string>
#include<vector>
#include<set>
#include<map>
#include<queue>
#include<numeric>
#include<functional>
#include<algorithm>
#include<bitset>
#include<tuple>
#include<unordered_set>
#include<random>
using namespace std;
#define INF (1<<29)
#define rep(i,n) for(int i=0;i<(int)(n);i++)
#define all(v) v.begin(),v.end()
#define uniq(v) v.erase(unique(all(v)),v.end())






int main() {
	ios::sync_with_stdio(0);
	cin.tie(0);
	
	double x;
	cin >> x;
	double ans = 0;
	for (int n = 500000000; n > 0;n--) {
		ans += 1.0 / ((x + n) *(x + n));
	}
	printf("%.9f\n", ans);

	return 0;
}