贪心即可

#include<bits/stdc++.h>
using namespace std;
#define int long long
const int N=1e5+10;
struct nd{int a,b;}ans[N];
int fac[110];
signed main()
{
	int l,r;scanf("%lld%lld",&l,&r);
	int m=0;fac[0]=1;
	for(int i=1;i<=60;i++)fac[i]=fac[i-1]*2;
	while(l<r)
	{
		for(int i=60;i>=0;i--)
			if(l%fac[i]==0&&l+fac[i]<=r)
			{
				ans[++m]={l,l+fac[i]};
				l+=fac[i];break;
			}
	}
	printf("%lld\n",m);
	for(int i=1;i<=m;i++)
		printf("%lld %lld\n",ans[i].a,ans[i].b);
	return 0;
}