#include <iostream>
#include <math.h>

using namespace std;
void Solve(int a)
{
	const double pi = 3.14;
	float ans;
	ans = 2 * pi * a;
	cout << ans;
}
int main()
{
	int x;
	cin >> x;
	Solve(x);
	return 0;
}
#include <bits/stdc++.h>
using namespace std;

int main() {
  long N, x, ans = 0;
  cin >> N;
  
  for (int i = N; i > 0; i--) {
    x = sqrt(i);
    x = x * x;
    if (i == x) {
      ans = i;
      break;
    }
  }
  
  cout << ans << endl;
}