# include <bits/stdc++.h>
# define ll long long
# define ld double
# define fi first
# define se second
# define pii pair<int, int>
# define pll pair<ll, ll>
# pragma GCC optimize("O3")
using namespace std;

int main() {
	int N;
	scanf("%d", &N);
	
	if(N%2 == 0) N--;
	printf("%d\n", N * N);
	for(int k=1;k<=N;k++) {
		for(int i=1;i<=N;i++) {
			printf("%d %d\n", i, k);
		}
	}
}