#include <string>
#include <cstdio>
#include <cstring>
#include <cmath>
#include <vector>
#include <queue>
#include <set>
#include <utility>
#include <algorithm>
#include <numeric>
#include <iostream>
#include <iterator>
#include <sstream>

using namespace std;

int main()
{
	double n;
	while(cin>>n) printf("%.15lf\n",n * 7.81481481481481481);
	return 0;
}