#include<iostream>
#include<string>
#include<algorithm>
#include<cctype>
#include<set>
#include<bitset>
#include<math.h>
#include<map>
#include<queue>
#include <iomanip>
using namespace std;


int main(){
    int x, n, r;
    cin >> x;
    if (x == 2) cout << 2 << endl;
    else if (x == 3) cout << 5 << endl;
    else if (x%2 == 0) cout << (x-4)/2*10 + 4 << endl;
    else cout << (x-3)/2*10 + 5 << endl;
}