#include<bits/stdc++.h>
using namespace std;

int main(){
  int n;
  cin>>n;
  if (n==2){
    cout<<-1<<endl;
    return 0;
  }
  vector<pair<int,int>> vp;
  for (int i=0;i<n*n;i++){
    vp.push_back({i,(i+1)%(n*n)});
    vp.push_back({i,(i+2)%(n*n)});
  }
  int m=2*n*n;
  cout<<m<<endl;
  for (int i=0;i<m;i++){
    cout<<vp[i].first+1<<" "<<vp[i].second+1<<endl;
  }
}