/*
TASK:necklace
LANG:C++
*/
#include<iostream>
using namespace std;
int main()
{
    
int n,i,br=0;
cin>>n;
if(n==2) {cout<<"1"<<endl;}
if(n==3) {cout<<"1"<<endl;}
if(n==4) {cout<<"3"<<endl;}
else
    { i=(((n*4)-2)/2);
}
     cout<<i;



    
    system("pause");
    return 0 ;
}

