#include <bits/stdc++.h>

using namespace std;

#define FOR(i, a, b) for(int i = (a); i < (b); i++)
#define RFOR(i, a, b) for(int i = (a) - 1; i >= (b); i--)
#define SZ(a) int(a.size())
#define ALL(a) a.begin(), a.end()
#define PB push_back
#define MP make_pair
#define F first
#define S second

typedef long long LL;
typedef vector<int> VI;
typedef pair<int, int> PII;
typedef double db;

void solve()
{
	int n, t, k;
	cin >> n >> t >> k;
	VI lens;
	VI a(n);
	FOR (i, 0, n)
		cin >> a[i];
	int x = 1;
	FOR (i, 1, n)
	{
		if (a[i] != a[i - 1])
		{
			lens.PB(x);
			x = 1;
		}
		else
			x++;
	}
	if (a.back() == a[0])
	{
		if (lens.empty())
			lens.PB(x);
		else
			lens[0] += x;
	}
	else
		lens.PB(x);
	int mx = *max_element(ALL(lens));
	if (mx < k)
		cout << -1 << '\n';
	else
	{
		int ans = 0;
		FOR (i, 0, SZ(lens))
		{
			ans += (lens[i] + k - 1) / k;
		}
		cout << ans << '\n';
	}
}

int main()
{
	ios::sync_with_stdio(0);
	cin.tie(0);
	
	int t;
	cin >> t;
	while (t--)
		solve();
	
	return 0;
}