#include<bits/stdc++.h>
using ll = long long;
#define endl '\n'
// #define int long long
using namespace std;
const int MAX = 2e5 + 5;

ll check(double x){
    ll res = 0;
    for (double i = 1; i <= x; i ++){
        res += floor(sqrt(x * x - i * i));
    }
    res *= 4ll;
    return res;
}
void solve(){
    ll s;
    cin >> s;
    double lk = 0.0, rk = 1e5;
    while (rk - lk > 1e-7){
        double mid = (lk + rk) / 2;
        if (check(mid) >= s) rk = mid;
        else lk = mid;
    }
    cout << lk;
}
signed main(){
    ios::sync_with_stdio(0);cin.tie(0);
    cout << fixed << setprecision(10);
    // int T=1;cin>>T;while(T--)
    solve();
}