#include <iostream>
#include <cmath>
#include <iomanip>

using namespace std;

int main(void)
{
        unsigned long long n;
        cin >> n;

        if (n < 4)
        {
                double annn = 1.41421360;
                cout << fixed << setprecision(8) << annn << endl;
                return 0;
        }
        if(n==4){
        	n=11;
		}


        unsigned long long k = 0;
        unsigned long long sum = 0;

        int num = 1;
        while(sum + k * 4 <= n)
        {
                sum += k * 4;
                sum += 4;
                num++;
                k = k + 2;
        }

        unsigned long long ksum = n - sum;
        ksum = ceil(ksum / 8.0);

        //cout << sum << endl;
        double r = sqrt(ksum * ksum + num * num);

//      cout << r << endl;

        cout << fixed << setprecision(8) << r << endl;
        return 0;
}