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

void solve(){
    int n,m;cin>>n>>m;
    vector<int>a(n),b(m);
    map<int,int>mp1,mp2;
    for(int i=0;i<n;i++){
        cin>>a[i];mp1[a[i]]++;
    }
    for(int i=0;i<m;i++){
        cin>>b[i];mp2[b[i]]++;
    }
    vector<int>a1,b1;
    for(int i=0;i<n;i++){
        if(mp2[a[i]]==0){
            a1.push_back(a[i]);
        }
    }
    for(int i=0;i<m;i++){
        if(mp1[b[i]]==0){
            b1.push_back(b[i]);
        }
    }
    sort(a1.begin(),a1.end());
    sort(b1.begin(),b1.end());
    int ans=0;
    int sum=a1.size();
    auto findr=[&](int pos){
        int i=a1[pos-1];
        auto pos1= std::lower_bound(b1.begin(), b1.end(),i);
        if(pos1==b1.end()){
            return sum-pos;
        }else{
            auto pos2= std::lower_bound(a1.begin(), a1.end(),*pos1);
            pos2--;
            int p2=pos2-a1.begin()+1;
            return p2-pos;
        }
    };
    auto findl=[&](int pos){
        int i=a1[pos-1];
        auto pos1= std::lower_bound(b1.begin(), b1.end(),i);
        if(pos1==b1.begin()){
            return pos-1;
        }else{
            pos1--;
            auto pos2= std::lower_bound(a1.begin(), a1.end(),*pos1);
            int p2=pos2-a1.begin()+1;
            return pos-p2;
        }
    };
    for(int i=0;i<sum;i++){
        int res=1;
        res+=findl(i+1);
        res+=findr(i+1);
        ans=max(ans,res);
    }
    if(ans!=0) cout<<ans<<"\n";
    else cout<<"Impossible\n";
}

signed main(){
    ios::sync_with_stdio(false);cin.tie(0);cout.tie(0);
    int T=1;
    cin>>T;
    while(T--){
        solve();
    }
    return 0;
}