#include <bits/stdc++.h>
using namespace std;
bool fl = 0;
bool mtest = 1;
void solve() {
  long double r;
  cin >> r;
  cout << 2 * 3.14159 * r << endl;
}
int main() {
  ios::sync_with_stdio(0);
  cin.tie(0);
  if (fl) {
    freopen("input.txt", "r", stdin);
    freopen("output.txt", "w", stdout);
  }
  int TE = 1;
  if (mtest) cin >> TE;
  while (TE--) solve();
  return 0;
}
