$Code :$

#include<bits/stdc++.h>
using namespace std;
int main(){
	ios::sync_with_stdio(false);
	cin.tie(0);
	cout.tie(0);
	unsigned long long a,b,book[70],now=0;
	int ans=0;
	cin>>a>>b;
	book[1]=1;
	for(int i=2;i<=64;i++){
		book[i]=book[i-1]*2;
//		cout<<book[i]<<" ";
	}
//	cout<<endl;
	for(int i=64;i>0;i--){
		if(now+book[i]-1>=a&&now+book[i]-1<=b){
			ans+=(i-1);
			break;
		}
		if(now+book[i]<=b){
			now+=book[i];
			ans++;
		}
	}
	cout<<ans;
	return 0;
}

如有不正确的地方，请神犇指正