#include<bits/stdc++.h>

#define pb push_back
#define x first
#define y second
#define all(a) (a).begin(), (a).end()

using namespace std;

typedef long long ll;
typedef pair<int, int> ii;

const int maxn = 1025;

int n;
vector<int> r, c, d1, d2;
vector<ii> ans;

int check(int x, int y) {
	return (r[x] + c[y] + d1[x + y] + d2[x - y + n] + 1) % 2;
}

int play(int x, int y) {
	if(!check(x, y)) {
		cout << "err\n";
		exit(0);
	}
	ans.pb({x, y});
	r[x]++, c[y]++, d1[x + y]++, d2[x - y + n]++;
}

void resi4() {
	play(0, 1);
	play(1, 3);
	play(0, 2);
	play(1, 0);
	play(1, 1);
	play(2, 3);
	play(0, 3);
	play(2, 0);
	play(2, 1);
	play(2, 2);
	play(3, 0);
	play(3, 2);
	play(3, 1);
	play(3, 3);
}

void resi3() {
	play(1, 2);
	play(2, 0);
	play(1, 1);
	play(0, 0);
	play(2, 2);
	play(2, 1);
	play(0, 1);
	play(0, 2);
	play(1, 0);	
}
	
void rek(int n) {
	if(n <= 2) {play(0, 0);return;}
	if(n == 3) {resi3();return;}
	if(n == 4) {resi4();return;}
	rek(n - 2);
	
	for(int i = 0;i < n - 3;i++) {
		if(check(i, n - 1))
			play(i, n - 1), play(i, n - 2);
		else play(i, n - 2), play(i, n - 1);
		
		if(check(n - 1, i))
			play(n - 1, i), play(n - 2, i);
		else play(n - 2, i), play(n - 1, i);
	}
	
	if(n % 2 == 1) {
		play(n - 2, n - 1);
		play(n - 3, n - 2);
		play(n - 1, n - 2);
		play(n - 2, n - 2);
		play(n - 3, n - 1);
		play(n - 1, n - 3);
		play(n - 2, n - 3);
		play(n - 1, n - 1);	
	} else {
		play(n - 3, n - 1);	
		play(n - 3, n - 2);
		play(n - 2, n - 1);
		play(n - 2, n - 3);
		play(n - 1, n - 3);
		play(n - 2, n - 2);
		play(n - 1, n - 2);
		play(n - 1, n - 1);
	}
}

int main() {
	cin >> n;
	vector<int> v(2 * n, 0);
	r = c = d1 = d2 = v;
	rek(n);
	cout << ans.size() << "\n";
	for(ii p : ans)
		cout << p.x + 1 << " " << p.y + 1 << "\n";
	return 0;
}