#include<iostream>
#include<stdio.h>
#include<algorithm>
#include<vector>
#include<string.h>
#include<math.h>
#include<map>
#include<iomanip>
#include<queue>

const long long INF = 1e6+7;
const long long MOD = 1e9+7;
const double PI=acos(-1);

using namespace std;

int main(){
	double n;
	cin >> n;
	double r2=n/PI;
	double r=sqrt(r2);
	cout << fixed << setprecision(10) << r << endl;
	return 0;
}