#include <stdio.h>
#include <bits/stdc++.h>
#include <atcoder/all>
using namespace atcoder;
using mint = modint998244353;
using namespace std;
#define rep(i,n) for (int i = 0; i < (n); ++i)
#define Inf32 1000000001
#define Inf64 1000000000000000001


int main(){
	ios::sync_with_stdio(false);
	cin.tie(nullptr);
	
	int n = 200000;
	cout<<n<<endl;
	vector<int> a,b;
	a.push_back(0);
	b.push_back(1);
	a.push_back(1);
	b.push_back(2);
	for(int i=4;i<=199998;i+=2){
		a.push_back(i-3);
		b.push_back(i-1);
		a.push_back(i-1);
		b.push_back(i);
	}
	a.push_back(199997);
	b.push_back(199999);
	assert((int)a.size()==n-1);
	rep(i,a.size()){
		cout<<a[i]+1<<' '<<b[i]+1<<endl;
	}
	
	
	return 0;
}