#include <bits/stdc++.h>
#define endl '\n'
#define int long long
using namespace std;

const int N = 1e6 + 5;

pair<int, int> a[N];
int b[N], c[N];

void solve() {
    int n, m;
    cin >> n >> m;
    for (int i = 1; i <= n; i++) {
        cin >> b[i];
    }
    for (int i = 1; i <= m; i++) {
        cin >> c[i];
    }
    c[m + 1] = INT_MAX;
    sort(c + 1, c + m + 1);
    int t = 0;
    for (int i = 1; i <= n; i++) {
        int x = *lower_bound(c + 1, c + m + 2, b[i]);
        if (x != b[i])
            b[++t] = b[i];
    }
    n = t;
    for (int i = 1; i <= n; i++) {
        a[i] = {b[i], 1};
    }
    for (int i = 1; i <= m; i++) {
        a[i + n] = {c[i], 2};
    }
    sort(a + 1, a + n + m + 1);
    
    int ans = 0;
    for (int r = 1, l = 1; r <= n + m; r++) {
        //cout << a[r].first << " \n"[r == n + m];
        if (a[r].second == 2) {
            l = r + 1;
            continue;
        }
        ans = max(ans, r - l + 1);
    }
    cout << (ans == 0 ? "Impossible" : to_string(ans)) << endl;
}

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

    int T = 1;
    cin >> T;
    while (T--) solve();

    return 0;
}