#include<bits/stdc++.h>
#define rep(i,n) for(int i=0; i< (n); i++)
using namespace std;
typedef long long ll;
typedef pair<int , int> P;
const ll inf = (1ll<<60);
//const int mod = 998244353;
const int mod = 1000000007;

int main(){
    int x;
    cin>>x;
    
    if(x==2) cout<<2<<endl;
    else if(x==3) cout<<5<<endl;
    else cout<<((x+1)/2-2)*10+4+(x%2)<<endl;
}