include<bits/stdc++.h> 
using namespace std; 
  
#define PI 3.1415 
  
double circumference(double r) 
{ 
    double cir = 2*PI*r; 
    return cir; 
} 
  
// driver function 
int main() 
{ 
  double r;
  cin>>r;
  cout << "Circumference = " 
       << circumference(r); 
  return 0; 
}  