#include <bits/stdc++.h>
using namespace std;

int main() {
    ios::sync_with_stdio(false);
    cin.tie(nullptr);

    const int digits = 9999;

    vector<int> a(digits * 10 / 3 + 2, 2);

    int n = a.size();

    int carry = 0;
    int predigit = 0;
    int nines = 0;

    string pi;

    for (int i = 0; i < digits; i++) {
        int q = 0;

        for (int j = n - 1; j >= 0; j--) {
            int x = 10 * a[j] + q * (j + 1);
            a[j] = x % (2 * (j + 1) - 1);
            q = x / (2 * (j + 1) - 1);
        }

        a[0] = q % 10;
        q /= 10;

        if (q == 9) {
            nines++;
        }
        else if (q == 10) {
            pi += char(predigit + 1 + '0');

            for (int k = 0; k < nines; k++)
                pi += '0';

            predigit = 0;
            nines = 0;
        }
        else {
            pi += char(predigit + '0');

            predigit = q;

            for (int k = 0; k < nines; k++)
                pi += '9';

            nines = 0;
        }
    }

    pi += char(predigit + '0');

    cout << pi[0] << ".";
    for (int i = 1; i < (int)pi.size(); i++) {
        cout << pi[i];
    }
}