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

#define For(i, a, b) for(int i = (a); i < (b); i++)
#define rep(i, n) For(i, 0, n)
#define rFor(i, a, b) for(int i = (a); i >= (b); i--)
#define ALL(v) (v).begin(), (v).end()
#define rALL(v) (v).rbegin(), (v).rend()

using lint = long long;
using ld = long double;

int INF = 2000000000;
lint LINF = 1000000000000000000;

struct SetupIo {
    SetupIo() {
        ios::sync_with_stdio(false);
        cin.tie(nullptr);
        cout << fixed << setprecision(15);
    }
} setupio;

unsigned int xorshift() {
    static unsigned int x = 123456789, y = 362436069, z = 521288629, w = 88675123;
    unsigned int t = (x ^ (x << 11));
    x = y;
    y = z;
    z = w;
    return (w = (w ^ (w >> 19)) ^ (t ^ (t >> 8)));
}

int rnd(int l, int r) {
    int res = xorshift() % (r - l);
    return res + l;
}

int main() {
    int n;
    cin >> n;
    ld n3 = ld(n) * ld(n) * ld(n);
    ld mny = sqrt(n3), mxy = sqrt(n3 + 1.0);
    int l = ceil(mny * 10000), r = floor(mxy * 10000);
    if (l >= r) {
        cout << mny << "\n";
        return 0;
    }
    auto get_x = [&]() -> ld {
        ld x = rnd(0, 10000);
        x /= 10000.0;
        return x;
    };
    auto get_y = [&]() -> ld {
        ld y = rnd(l, r);
        y /= 10000.0;
        return y;
    };
    auto in = [&](ld x, ld y) -> bool {
        ld fx = sqrt(x * x * x + n3);
        return y <= fx;
    };
    int all = 10000000, cnt = 0;
    rep(_, all) {
        ld x = get_x(), y = get_y();
        if (in(x, y)) {
            cnt++;
        }
    }
    cout << mny + ld(cnt) / ld(all) * (mxy - mny) << "\n";
}