#include <algorithm>
#include <cmath>
#include <complex>
#include <iostream>
#include <map>
#include <queue>
#include <set>
#include <string>
#include <vector>
#define rep(i, n) for (int i = 0; i < (n); i++)
#define rrep(i, n) for (int i = (n)-1; i >= 0; i--)
using namespace std;
typedef long long int lli;
typedef pair<lli, lli> P;
lli MOD = 1000000007;
int main()
{
    double pi = 4 * atan(1);
    double sum = 0;
    double x;
    cin >> x;

    rep(i, 5000000)
    {
        double n = (double)(i + 1);
        sum += 1e10 * (2 * x * n + x * x) / n / n / (x + n) / (x + n);
    }
    printf("%.10f\n", (pi * pi / 6) - sum / 1e10);
}