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

long long calc(double r){
    int x = r;
    long long ans = 0;
    for(int y = 1; y <= r; y++){
        while(1LL * x * x + 1LL * y * y > 1LL * r * r)
            --x;
        ans += x;
    }
    return 4 * ans;
}
int main() {
    cin.tie(0);cin.sync_with_stdio(0);
    cout.tie(0);cout.sync_with_stdio(0);

    int s; cin>>s;
    double L = 0, R= 1e6 + 10, ans;
    for(int rep = 0; rep < 120; rep++){
        double md = (L + R) * 0.5;
        if(calc(md) >= s)
            ans= md, R= md;
        else
            L= md;
    }
    cout<<fixed<<setprecision(10);
    cout<<ans<<"\n";

}