#include<iostream>
#include<cstdio>
#include<vector>
#include<cmath>
#define N 100000
using namespace std;
int read()
{
	char c=0;
	int sum=0;
	while (c<'0'||c>'9') c=getchar();
	while ('0'<=c&&c<='9') sum=sum*10+c-'0',c=getchar();
	return sum;
}
struct reads
{
	int x,y;
};
reads tong[N+1];
int n,k,length,st[N+1],leng;
void adder(int x,int y)
{
	tong[++length]=(reads){x,y};
	return;
}
int main()
{
	int d;
	n=read(),k=read(),d=sqrt(n);
	for (int i=1;i<=n;++i)
		if (i%d==0)
			st[++leng]=i;
	for (int i=1;i<=leng;++i)
		for (int j=i+1;j<=leng;++j)
			adder(st[i],st[j]);
	for (int i=1;i<=st[1]-2;++i) adder(i,st[1]);
	for (int i=1;i<=leng-1;++i)
		for (int j=st[i]+2;j<=st[i+1]-2;++j)
			adder(st[i],j),adder(j,st[i+1]);
	for (int i=st[leng]+2;i<=n;++i) adder(st[leng],i);
	printf("%d\n",length);
	for (int i=1;i<=length;++i) printf("%d %d\n",tong[i].x,tong[i].y);
	return 0;
}