#include <bits/stdc++.h>
#define N 1000009
#define int long long
using namespace std;
int n, m, a[N];

bool ok(int mid) {
	int sum = 0;
	for (int i = 1; i <= n; i++) {
		int tmp = mid - 2 * a[i] - 1;
		if (tmp <= 0)
			continue;
		if (tmp >= a[i] + 1)
			sum += mid / 2;
		else
			sum += tmp;
		if (sum >= m)
			return 1;
	}
	return 0;
}

void solve() {
	scanf("%lld%lld", &n, &m);
	for (int i = 1; i <= n; i++)
		scanf("%lld", &a[i]);
	int l = 0, r = 1000000000000000000, ans = 0;
	while (l <= r) {
		int mid = (l + r) >> 1;
		if (ok(mid))
			ans = mid, r = mid - 1;
		else
			l = mid + 1;
	}
	printf("%lld\n", ans);
}

signed main() {
	int t;
	scanf("%lld", &t);
	while (t--)
		solve();
	return 0;
}