#include <bits/stdc++.h>

typedef long double ld;
typedef long long ll;
using namespace std;
int di[] = {1, 0, -1, 0, 0, 1, -1, 1};
int dj[] = {0, 1, 0, -1, -1, 0, 1, -1};
const ll oo = 1e18, MOD = 1e9 + 7;
const int N = 2e5+ 5, M = 30005;
#define EPS 1e-9

int t, m, ans;
ll n;

int main() {
    //ios_base::sync_with_stdio(0), cin.tie(0), cout.tie(0);
    //freopen("output.txt", "w", stdout);
    cin >> n;
    n--;
    /*for(int i = 1; i < n ;++i){
        int u,v;
        cin >> u >> v;
        g[u].push_back(v);
        g[v].push_back(u);
    }*/
    map<ll,int> mp;
    vector<ll>sq;
    for(int i=0;i<N;i++)
    {
        sq.push_back(1ll*i*i);
        mp[1ll*i*i]=i;
    }
    ld lo=0,hi=N;
    while(hi-lo>EPS) {

        ld mid = (lo + hi) / 2.0;
        ll y = 1.0 * mid * mid;
        ll id1 = 0, id2 = 0, mx = 0;
        for (auto x:sq) {
            if(!x)continue;
            if (x > y)break;
            int pos = upper_bound(sq.begin(), sq.end(), y - x) - sq.begin() - 1;

            if (pos == -1)continue;
            else {
                mx+=4*mp[sq[pos]];
            }

        }
        //cout<<lo<<" "<<hi<<" "<<mid<<" "<<mx<<" "endl;
        if (mx >=n)
        {
            hi=mid;
        }
        else lo=mid;

    }
    cout<<fixed<<setprecision(11)<<lo;

    return 0;
}