AC

#include<bits/stdc++.h>
using namespace std;
int n;
int main(){
	cin>>n;
	if(n==1) cout<<2<<"\n";
	else if(n==2) cout<<4<<"\n";
	else{
		cout<<4+(3+3+(n-3))*(n-2)/2<<"\n";
	}
	return 0;
}