#include<bits/stdc++.h>
using namespace std;
#define endl '\n'
#define ll long long
#define ld long double

const int N = 2e5 + 5;
const ld eps = 0.000000001;

int main() {
    ios_base::sync_with_stdio(false); cin.tie(NULL);

    ll n;
    cin>> n;
    ld l = 0, r = 20000;
    while(l <= r-eps) {
        ld mid = (l+r)/2;

        ld height = 1;
        ll cnt = 0;
        while(height <= mid) {
            ld val = mid*mid - height*height;
            ld base = sqrtl(mid*mid - height*height);
            ll baseint = base;
            baseint += 5;
            while(baseint * baseint > val) baseint--;
            baseint *= 2;
            cnt += baseint;
            height++;
            if(cnt * 2 > n) break;
            //cout<< mid << " " << cnt*2 << endl;
        }
        //cout<< cnt*2<< endl;
        cnt *= 2;
        if(cnt > n) {
            r = mid;
            //cout<< mid << " yes" << endl;
        }
        else l = mid;
    }
    cout<< setprecision(12) << fixed << r << endl;
}