#include <bits/stdc++.h>
#include <atcoder/all>
using mint = atcoder::static_modint<998244353>;
//using mint = atcoder::static_modint<1000000007>;
using namespace std;
using namespace atcoder;
using ld = long double;
using ll = long long;
#define mp(a,b) make_pair(a,b)
#define rep(i,s,n) for(int i=s; i<n; i++)
const vector<int> dx{1,0,-1,0},dy{0,1,0,-1};

int main(){
    ll n;
    cin >> n;
    n*=n*n;
    ld ans=0;
    ll m=1000000;
    ld h=1/(ld)m;
    rep(i,0,m){
        ld x=i/(ld)m;
        ans+=sqrt(x*x*x+n)*h;
    }
    cout << setprecision(16) << ans;
}