package main

import (
	"bufio"
	"fmt"
	"os"
)

func main() {
	in := bufio.NewReader(os.Stdin)
	out := bufio.NewWriter(os.Stdout)
	defer out.Flush()

	var n int
	fmt.Fscan(in, &n)

	m := (n + 2) / 2
	fmt.Fprintln(out, m)

	for i := 1; i <= n; i++ {
		if i <= m {
			fmt.Fprintln(out, 1, i)
		} else {
			fmt.Fprintln(out, i-m+1, m)
		}
	}
}