#include <bits/stdc++.h>  
using namespace std;  

#define int long long  

void solve()
{
	int n, m;
	cin >> n >> m;
	vector<pair<int, int>> a(n + m);
	for(int i = 0; i < n; ++i) {
		int x;
		cin >> x;
		a[i].first = x;
		a[i].second = 1;
	}
	for(int i = n; i < n + m; ++i) {
		int x;
		cin >> x;
		a[i].first = x;
		a[i].second = 0;
	}

	sort(a.begin(), a.end());

	int ans = 0, cur = 0, last = -1;
	for(auto &[x, c] : a) {
		if(c == 0) {
			ans = max(ans, cur);
			cur = 0;
			last = x;
		} else if(x != last) {
			++cur;
		}
	}
	ans = max(ans, cur);
	if(ans != 0)
		cout << ans << '\n';
	else
		cout << "Impossible\n";
}


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

    int T;
    cin >> T;
    while(T--) solve();
    return 0;
}