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#include <bits/stdc++.h>

using namespace std;

int edge[101][2];

int main(){
	cin.tie(0);
	cout.tie(0);
	ios_base::sync_with_stdio(false);

	for (int i = 1; i <= 100; ++i)
	{
		edge[i][0] = edge[i][1] = -1;
	}

	long long k;
	cin >> k;

	// wierzchołki 1, 2 i 3
	edge[99][0] = 100;
	edge[98][0] = 100;
	edge[98][1] = 99;

	long long cur = k;
	int cur_v = 1;
	while(true){
		if(cur == 1){
			edge[cur_v][0] = 100;
			break;
		}
		if(cur == 2){
			edge[cur_v][0] = 98;
			break;
		}

		if(cur == 3){
			edge[cur_v][1] = 99;
			edge[cur_v][0] = 98;
			break;
		}
		if(cur >= 4){
			if(cur % 2 == 0){
				edge[cur_v][0] = cur_v + 1;
				edge[cur_v][1] = cur_v + 2;
				edge[cur_v + 1][0] = 98;
				edge[cur_v + 1][1] = cur_v + 2;
				cur_v += 2;
				cur = cur / 2 - 1;
			}
			else{
				edge[cur_v][0] = cur_v + 1;
				edge[cur_v][1] = cur_v + 2;
				edge[cur_v + 1][0] = 99;
				edge[cur_v + 1][1] = cur_v + 2;
				cur_v += 2;
				cur = cur / 2;
			}
		}
	}


	cout << 100 << endl;

	for (int i = 1; i <= 100; ++i)
	{
		cout << edge[i][0] << " " << edge[i][1] << endl;
	}


}