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

signed main() {
    int n;
    cin >> n;
    long double l = 1, r = n/2;
    while (l + 1e-9 < r) {
        long double m = (l + r) / 2;
        int sum = 0;
        for(int i = 1; i <= m; i++) {
            for(int j = 1; j <= m; j++) {
                if(i*i + j*j <= m*m) {
                    sum++;
                }
            }
        }
        if(sum * 4 >= n) {
            r = m;
        } else {
            l = m;
        }
    }
    cout << fixed << setprecision(10) << r << endl;
    return 0;
}