#include <iostream>
#include <algorithm>
#include <map>
#include <set>
#include <queue>
#include <stack>
#include <numeric>
#include <bitset>
#include <cmath>

static const int MOD = 998244353;
using ll = long long;
using u32 = unsigned;
using u64 = unsigned long long;
using namespace std;



int main() {
    long double x;
    cin >> x;
    printf("%.15Lf\n", riemann_zeta(x));
    return 0;
}