#include <bits/stdc++.h>
#define int long long

using namespace std;

inline int read () {
    int w = 1, s = 0; char ch = getchar ();
    for (; ! isdigit (ch); ch = getchar ()) if (ch == '-') w = -1;
    for (; isdigit (ch); ch = getchar ()) s = (s << 1) + (s << 3) + (ch ^ 48);
    return s * w;
}

void solve () {
	int n = read ();

    printf ("%lld\n", 2 * n - 1);
    for (int i = 1; i <= 2 * n - 1; i ++) {
        printf ("1 %lld\n", i);
    }
} 

signed main () {
	// ios::sync_with_stdio (false);
    // cin.tie (nullptr);
    
	int T = 1; 
	// cin >> T;
	// T = read ();

	while (T --) {
		solve ();
	}
	
	return 0;
}