#![allow(unused_imports,non_snake_case,dead_code)]
use std::{cmp::Reverse as Rev,ops::Range,collections::*,iter::*,mem::swap};
use proconio::{marker::*,*};



#[fastout]
fn main(){
    input!{
        n:usize,
    }

    if n<=2{
        println!("-1");
        return;
    }

    let n2=n*n;
    let to=|x:usize|{
        if x%n2==0{
            n2
        } else{
            x%n2
        }
    };
    println!("{}",n*n*2);
    for i in 0..n{
        for j in 0..n{
            let u=i*n+j+1;
            println!("{} {}",u,to(u+n2-n));
            println!("{} {}",u,to(u+n2-1));
        }
    }
}