#include<bits/stdc++.h>
using namespace std;
int n; 
signed main()
{
	freopen("Sample.in","w",stdout);
	printf("70000\n");
	for (int i = 2; i <= 70000; i++)
		printf("%d %d\n", i, i >> 1);
	return 0;
}

卡掉了题解： https://www.luogu.com.cn/article/62lutdan