#include<bits/stdc++.h>
#define Yukinoshita namespace
#define Yukino std
using Yukinoshita Yukino;
int read()
{
	int s=0,w=1;
	char ch=getchar();
	while(ch<'0'||ch>'9') w=ch=='-'?-1:1,ch=getchar();
	while(ch>='0'&&ch<='9') s=s*10+ch-'0',ch=getchar();
	return s*w;
}
const int mxn=2e6+5;
int a[mxn];
deque<pair<int,int>> q;
int sum,k;
void push(int c)
{
	if(q.size()&&c==q.back().first)
		sum-=(q.back().second+k-1)/k,
		q.back().second++,
		sum+=(q.back().second+k-1)/k;
	else
		sum++,q.push_back({c,1});
}
void pop()
{
	if(q.front().second==1)
		sum--,q.pop_front();
	else
		sum-=(q.front().second+k-1)/k,
		q.front().second--,
		sum+=(q.front().second+k-1)/k;
}
int main()
{	
	int T=read();
	while(T--)
	{
		q.clear();
		sum=0;
		int n=read(),m=read(),i,mn=1e9;
		k=read();
		for(i=1;i<=n;i++)
			a[i]=a[i+n]=read();
		for(i=n*2;i>n;i--)
			push(a[i]);
		for(;i;i--)
		{
			pop();
			push(a[i]);
			if(q.back().second>=k)
				mn=min(mn,sum);
		}
		printf("%d\n",mn==1e9?-1:mn);
	}
}