#include<bits/stdc++.h>
using namespace std;
char calc(string s){
	return *max_element(s.begin(),s.end());
}
void solve(){ int la,ra,lb,rb;
	cin>>la>>ra>>lb>>rb; char ans='0';
	if (ra+rb-la-lb>9) return puts("9"),void();
	for (int i=la+lb;i<=ra+rb;i++)
		ans=max(ans,calc(to_string(i)));
	printf("%c\n",ans);
}
int main(){
	ios::sync_with_stdio(0); cin.tie(0); cout.tie(0);
	int T;cin>>T;while (T--) solve();
	return 0;
}