#include <bits/stdc++.h>
using namespace std;
double a = 0.28318530717958623200;
double ans1;
int ans2, k;
int tt, x;
int main() {
  scanf("%d", &x);
  ans1 = x * a;
  k = ans1;
  ans2 = 6 * x + k;
  tt = ans2 % 10;
  ans1 = ans1 - k + tt;
  ans2 = (ans2 - tt) / 10;
  if (ans2 >= 10)
    printf("%d%.20llf", ans2, ans1);
  else
    printf("%.20llf", ans1);
  return 0;
}
