#include<bits/stdc++.h>

using namespace std;

typedef long long ll;

const ll MX = (1<<20);

ll arr[MX] , vi[MX];

ll getsum(ll L , ll R){
    L--;
    R *= (R+1); R/=2;
    L *= (L+1); L/=2;
    return R - L;
}
int main(){
    ll T;
    cin>>T;
    while(T--){

        ll total , current , maxy , dif;

        scanf("%lld %lld %lld %lld",&total,&current,&maxy,&dif);

        for(ll j = 1 ; j <= current ; j++)
            scanf("%lld",&arr[j]);

        sort(arr+1 , arr+1+current);

        set < ll > sol;

        ll rem = total - current;

        ll last = 0 , fakss = 0;

        for(ll j = 1 ; j <= current ; j++){

            if(j == 1 || arr[j] - last > dif){

                if(j != current && arr[j + 1] - arr[j] <= dif){
                    sol.insert(arr[j]);
                    sol.insert(arr[j + 1]);
                    last = arr[j + 1];
                    j++;
                    continue;
                }
                else{
                    if(rem == 0){
                        fakss = 1;
                        break;
                    }
                    --rem;
                    sol.insert(arr[j]);
                    if(arr[j] + dif > maxy){
                        if(maxy == arr[j])
                            sol.insert(arr[j] - 1);
                        else sol.insert(maxy);
                        break;
                    }
                    else{
                        sol.insert(arr[j] + dif);
                        last = arr[j] + dif;
                        continue;
                    }

                }

            }
            else{
                sol.insert(arr[j]);
                last = arr[j];
            }

        }
        long long ans = 0;
        if(sol.empty()) fakss = 1;

        else{

            long long st = maxy;

            if(rem == 1) st = min(st , *sol.rbegin() + dif);

            vector < ll > sorted (sol.begin() , sol.end());

            reverse(sorted.begin() , sorted.end());

            for(auto V : sorted){
                ans += V;
                if(rem == 0 || st < 1) continue;
                if(st - V <= rem){
                    rem -= (st - V);
                    ans += getsum(V + 1 , st);
                    st = V - 1;
                }
                else{
                    ans += getsum(st - rem + 1 , st);
                    rem = 0;
                }
            }
            if(st >= rem && rem > 0){
                ans += getsum(st - rem + 1 , st);
                rem = 0;
            }

        }
        if(rem > 0) fakss = 1;
        if(fakss) puts("-1");
        else{
            cout<<ans<<endl;
        }
    }

}