#include <iostream>
#include <fstream>
using namespace std;

ifstream f("dame.in");
ofstream g("dame.out");

int main()
{
	int n;
	f >> n;

	g << n << endl;
		int rest=n%6;
		int t=1;
		if(rest!=2 && rest!=3){
			for(int i=2; i<=n; i+=2) {g << t << " " << i << "\n"; t++; }
			for(int i=1; i<=n; i+=2) {g << t << " " << i << "\n"; t++; }
			g<<"\n";
		}
		if(rest==2){
			for(int i=2; i<=n; i+=2) {g << t << " " << i << "\n"; t++; }
			g << t << " " << 3 << endl; t++;
			g << t << " " << 1 << "\n"; t++;
			for(int i=7;i<=n;i+=2) {g << t << " " << i << "\n"; t++; }
			g <<t << " " << 5;
			g << "\n";
		}
		if(rest==3){
			for(int i=4; i<=n; i+=2) {g << t << " " << i << "\n"; t++; }
            g << t << " " << 2 << endl; t++;
			for(int i=5;i<=n;i+=2) {g << t << " " << i << "\n"; t++; }
			g << t << " " << 1 << endl; t++;
			g << t << " " << 3 << "\n"; t++;
		}
}