#include<bits/stdc++.h>
using namespace std;
using ll = long long;
#define all(a) (a).begin(), (a).end()
#define pb push_back
#define fi first
#define se second
mt19937_64 rng(chrono::system_clock::now().time_since_epoch().count());
const ll MOD1000000007 = 1000000007;
const ll MOD998244353 = 998244353;
const ll MOD[3] = {999727999, 1070777777, 1000000007};
const ll LINF = 1LL << 60LL;
const int IINF = (1 << 30) - 2;

using ld = long double;

void solve(){
    ld N; cin >> N;

    function<ld(ld)> f = [&](ld x){
        return sqrt(x*x*x + N*N*N);
    };

    ld ans = 0;
    int n = 1e7;
    for(int k=1; k<=n; k++){
        ans += f((ld)k/(ld)n);
    }

    cout << fixed << setprecision(10) << ans/(ld)n << endl;
}

int main(){
    cin.tie(nullptr);
    ios::sync_with_stdio(false);
    
    int T=1;
    //cin >> T;
    while(T--) solve();
}