#include <iostream>
#include <fstream>


const int NMAX = 1002;


int board[NMAX][NMAX];


int main() {

	std::ifstream in("dame.in");
	std::ofstream out("dame.out");

	int N;
	in >> N;

	int i = 1;
	int j = 1;

	out << N << '\n';
	while (j <= N){
		out << i << ' ' << j << '\n';
		++i;
		j += 2;
	}

	j = 2;
	while (i <= N) {
		out << i << ' ' << j << '\n';
		++i;
		j += 2;
	}

	system("PAUSE");
	return 0;
}