#include<iostream>
#include<cmath>
using namespace std;
int main(){

  double a;
  
  while(cin >> a){

    double s[10] ={},ans = 0;

    for(int i = 1; i <= 10; i++){
      int si = 0, bo = 0;
      if(i == 1){
        s[i] = a;
      }
      else if(i % 2 == 0){
        si = pow(2, i/2);
        bo = pow(3, i/2 - 1);
        s[i] = a * (si / bo);
      }
      else{
        si = pow(2, i/2);
        bo = pow(3, i/2);
        s[i] = a * (si / bo);
      }

      ans += s[i];
    }

    cout << ans << endl;
  }
  
}