package main

import . "fmt"

func main() {
	var n int
	Scan(&n)
	nn := n*n
	if nn < 5 {
		Println(-1)
		return
	}
	ans := [][]any{}
	for i := 0; i < nn; i++ {
		ans = append(ans, []any{i+1, (i+1)%nn+1})
		ans = append(ans, []any{i+1, (i+n)%nn+1})
	}
	Println(len(ans))
	for _, line := range ans {
		Println(line...)
	}
}