#include<iostream>
#include<cassert>
using namespace std;
int main()
{
	ios::sync_with_stdio(false);
	cin.tie(nullptr);
	int N;
	cin>>N;
	if(N<=2)
	{
		cout<<-1<<endl;
		return 0;
	}
	cout<<N*N*2<<"\n";
	for(int i=0;i<N;i++)for(int j=0;j<N;j++)
	{
		int u=i*N+j+1;
		cout<<u<<" "<<(u+1-1)%(N*N)+1<<"\n";
		cout<<u<<" "<<(u+N-1)%(N*N)+1<<"\n";
	}
}