//sample code
#include <cstdio>
#include <iostream>
#include <cmath>
#include <string>
#include <list>
#include <vector>
#include <algorithm>
#include <functional>
#include <utility>
#include <set>
#include <map>
#include <complex>
#include <queue>
#include <stack>
#include <cstdlib>
#include <ctime>
#include <cstring>
#include <string.h>
using namespace std;
typedef unsigned int uint;
typedef long long int64;
typedef unsigned long long uint64;
typedef unsigned short ushort;
typedef unsigned char uchar;
typedef pair<int,int> ipair;
typedef vector<int> VI;
typedef vector<string> VS;
typedef vector<double> VD;
#define SIZE(A) ((int)(A.size()))
#define LENGTH(A) ((int)(A.length()))
#define MP(A,B) make_pair(A,B)
const double pi=acos(-1.0);
const double eps=1e-11;
#define FOR(i,a,b) for(int i=(a);i<=(b);++i)
#define REP(i,a) for(int i=0;i<(a);++i)
#define ALL(a) (a).begin(),(a).end()
template<class T> T sqr(const T &x) { return x*x; }
template<class T> T lowbit(const T &x) { return (x^(x-1))&x; }
template<class T> int countbit(const T &n) { return (n==0)?0:(1+countbit(n&(n-1))); }
template<class T> void ckmin(T &a,const T &b) { if (b<a) a=b; }
template<class T> void ckmax(T &a,const T &b) { if (b>a) a=b; }
int main()
{
unsigned long tc, N,K,D,M,sum,ele,a;
scanf("%d",&tc);
VI V;
while(tc--)
{
scanf("%lu%lu%lu%lu",&a, &K, &D, &M);
sum =0;
//cout<<a<<endl;
for(int i=0;i<(a);++i)
{
scanf("%lu",&ele);
//cout<<ele<<" ";
sum = sum +ele;
V.push_back(ele);
}
//cout<<sum<<endl;
sort(V.begin(),V.begin()+N);
// cout<<V[4]<<endl;
cout<<((sum-V[1])*M)<<endl;
}
return 0;
}
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