#include <vector>
#include <iostream>
#include <string>
#include <sstream>
#include <algorithm>
#include <utility>
#include <map>

using namespace std;
typedef long long ll;
typedef pair<ll,ll> P;

int main(){
	double n;
	cin >> n;
	cout << n * 3.5 << endl;
	return 0;
}