#include<bits/stdc++.h>
using namespace std;
const double eps = 5e-7;
long long get(double s)
{
    long long ans = 0;
    double p = s * s;
    for(int i = 1;i <= s;i++) {
        ans += 4*((int)(sqrt(p - i*i))) ;
    }
    return ans;
}
int main()
{
    int s;cin >> s;
    double l = 0 , r = sqrt(s) ;
    while((r - l) / l > eps) {
        double md = (l + r) / 2;
        if(get(md) >= s) r = md;
        else l = md;
    }
    printf("%.12lf\n",(l + r) / 2);
    return 0;
}