#include<bits/stdc++.h>
using namespace std;
long long T;
int main(){
	cin>>T;
	while(T--){
		long long n,m,k,s,minn=1e9;
		long long a[100009];
		cin>>n>>m>>k>>s;
		for(int i=1;i<=n;i++){
			cin>>a[i];
			minn=min(minn,a[i]);
		}
		if (minn<=s) cout<<0<<endl;
		else if(m==0) cout<<"Impossible!"<<endl;
		else cout<<ceil(1.0*(minn-s)/m)<<endl;
	}
	return 0;
}