#include 
#include 
#include 
#include 
using namespace std;
const int maxn = 105;
const int INF = 1e8;
int n, k;
int dp[maxn][1101];
int kg[maxn];
int rek(int friends, int left) {
    if(friends == 0 and left > 0) {
        return INF;
    }
    if(left == 0) {
        return 0;
    }
    if(dp[friends][left] != -1) {
        return dp[friends][left];
    }
    int res = INF;
    for(int i = 0; i < n; i++) {
        if(kg[i] != -1) {
            if(left - (i + 1) >= 0) {
                res = min(res, rek(friends - 1, left - (i + 1)) + kg[i]);
            }
        }
    }
    return dp[friends][left] = res;
}
int main()
{
    int t;
    cin >> t;
    
    while(t--) {
        cin >> k >> n;
        for(int i = 0; i < n; i++) {
            cin >> kg[i];
        }
        for(int i = 0; i <= k; i++) {
            for(int j = 0; j <= 1005; j++) {
                dp[i][j] = -1;
            }
        }
        int res = rek(k, n);
        if(res >= INF) {
            cout << -1 << endl;
        }
        else {
            cout << res << endl;
        }
    }
    return 0;
}