#include<bits/stdc++.h>

#define rep(i,s,n) for(int i = int(s); i < int(n); i++)
#define rrep(i,s,n) for(int i = int(n) - 1; i >= int(s); i--)
#define all(v) (v).begin(), (v).end()

using ll = long long;
using ull = unsigned long long;
using ld = long double;

template<class T>
bool chmin(T &a, T b) {
    if(a <= b) return false;
    a = b;
    return true;
}

template<class T>
bool chmax(T &a, T b) {
    if(a >= b) return false;
    a = b;
    return true;
}

using namespace std;

int f(ll x){
    int v = 0;
    while(x > 0){
        chmax(v, (int)(x % 10));
        x /= 10;
    }
    return v;
}

void solve(){
    int l1, r1, l2, r2; cin >> l1 >> r1 >> l2 >>  r2;
    int l = l1 + l2;
    int r = r1 + r2;
    if (r - l >= 20){
        cout << '9' << '\n';
    }else{
        int ans = 0;
        rep(i,l,r+1){
            chmax(ans, f(i));
        }
        cout << ans << '\n';
    }
}

int main() {
    std::cin.tie(nullptr);
    std::ios::sync_with_stdio(false);

    int t; cin >> t;
    while(t--) solve();
}