#include <iostream>
#include <iomanip>

using namespace std;

int main() {

  double n;
  cin >> n;
  cout << fixed << setprecision(20) << (2 * (n) * 3.14159265359);
  return 0;
}

#include <iostream>
#include <vector>
#include <algorithm>
#include <cmath>
#include <iomanip>

using namespace std;
using ll = long long;


int main() {
    int x;
    cin >> x;
    int a = x / 500;
    int b = (x % 500) / 5;
    cout << a * 1000 + b * 5 << endl;
}