#include <bits/stdc++.h>

#define ll long long
#define fi first
#define se second

using namespace std;

const int maxn = 1e5 + 10;

void nep(int n){
	if(n == 1){
		cout << "1 1\n";
		return;
	}
	
	nep(n - 2);
	
	for(int i = 0; i < (n - 3) / 2; i += 2){
		cout << n << ' ' << i + 1 << "\n";
		cout << n - 1 << ' ' << i + 1 << "\n";
		cout << i + 1 << ' ' << n - 1 << "\n";
		cout << i + 1 << ' ' << n << "\n";
		cout << n - 1 << ' ' << i + 2 << "\n";
		cout << n << ' ' << i + 2 << "\n";
		cout << i + 2 << ' ' << n << "\n";
		cout << i + 2 << ' ' << n - 1 << "\n";
	}
	
	cout << n << ' ' << n - 1 << "\n";
	cout << n << ' ' << n - 2 << "\n";
	cout << n - 2 << ' ' << n << "\n";
	cout << n - 1 << ' ' << n << "\n";
	cout << n - 2 << ' ' << n - 1 << "\n";
	cout << n - 1 << ' ' << n - 1 << "\n";
	cout << n - 1 << ' ' << n - 2 << "\n";
	cout << n << ' ' << n << "\n";
}

void par(int n){
	if(n == 2){
		cout << "2 2\n";
		return;
	}
	
	par(n - 2);
	
	cout << n << ' ' << n - 1 << "\n";
	cout << n - 1 << ' ' << n - 1 << "\n";
	cout << n - 1 << ' ' << n << "\n";
	cout << n << ' ' << n << "\n";
	
	for(int i = 0; i < n - 3; i++){
		cout << n << ' ' << i + 1 << "\n";
		cout << n - 1 << ' ' << i + 1 << "\n";
		cout << i + 1 << ' ' << n - 1 << "\n";
		cout << i + 1 << ' ' << n << "\n";
	}
	
	if(n == 4){
		cout << n << ' ' << n - 2 << "\n";
		cout << n - 1 << ' ' << n - 2 << "\n";
		cout << n - 2 << ' ' << n - 1 << "\n";
		cout << n - 2 << ' ' << n << "\n";
	}
	else {
		cout << n - 1 << ' ' << n - 2 << "\n";
		cout << n << ' ' << n - 2 << "\n";
		cout << n - 2 << ' ' << n << "\n";
		cout << n - 2 << ' ' << n - 1 << "\n";
	}
}

int main(){
	ios_base::sync_with_stdio(0);
	cin.tie(0);
	
	int n;
	
	cin >> n;
	
	if(n % 2 == 1){
		cout << n * n << "\n";
		
		nep(n);
	}
	else {
		cout << n * n - 3 << "\n";
		
		par(n);
	}

	return 0;
}