#include<bits/stdc++.h>
#define Gc() getchar() 
#define Me(x,y) memset(x,y,sizeof(x))
#define Mc(x,y) memcpy(x,y,sizeof(x))
#define d(x,y) ((m)*(x-1)+(y))
#define R(n) (rnd()%(n)+1)
#define Pc(x) putchar(x)
#define LB lower_bound
#define UB upper_bound
#define fi first
#define se second
using namespace std;using ll=long long;using db=double;using lb=long db;using ui=unsigned;using ull=unsigned long long;using pii=pair<int,int>;using LL=__int128;
const int N=1e6+5,M=100+5,K=600+5,mod=1e9+7,Mod=mod-1;const db eps=1e-9;const int INF=1e9+7;mt19937 rnd(time(0));
int n,m,k,A[N];
void Solve(){
	int i,j;
	scanf("%d%d%d",&n,&m,&k);
	for(i=1;i<=n;i++) scanf("%d",&A[i]);
	vector<int> B;B.emplace_back(1);
	for(i=2;i<=n;i++) if(A[i]==A[i-1]) B.back()++;else B.emplace_back(1);
	if(B.size()>1&&A[1]==A[n]) B.front()+=B.back(),B.pop_back();
	int flag=0;
	for(int i:B) if(i>=k){flag=1;break;}
	if(!flag){puts("-1");return;}
	int ans=0;for(int i:B) ans+=(i+k-1)/k;
	printf("%d\n",ans);
}
int main(){
	int t;
	scanf("%d",&t);
	// t=1;
	while(t--) Solve();
	cerr<<clock()*1.0/CLOCKS_PER_SEC<<'\n';
}