#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using ull = unsigned long long;
using pii = pair<int, int>;
using vi = vector<int>;
using vll = vector<ll>;
using vpii = vector<pii>;
#define repn(i, n) for (int i = 1; i <= (int)n; i++)
#define rep(i, n) for (int i = 0; i < (int)n; i++)
#define repr(i, m, n) for (int i = (int)m; i <= (int)n; i++)
#define repd(i, m, n) for (int i = (int)m; i >= (int)n; i--)
#define chmax(a, b) a = max(a, b)
#define chmin(a, b) a = min(a, b)
#ifdef LILYWHITE
    #define eprintf(...) { fprintf(stderr, __VA_ARGS__); fflush(stderr); }
#else
    #define eprintf(...) ;
#endif
const int __attribute__((unused)) INF = 0x3f3f3f3f;
template <typename T> inline T rd(T &x) {
    x = 0;
    T neg = 1;
    char c = 0;
    while (c < '0' || c > '9') {
        if (c == '-')
            neg = -1;
        c = getchar();
    }
    while (c >= '0' && c <= '9') {
        x = x * 10 + c - 48;
        c = getchar();
    }
    x *= neg;
    return x;
}
template <typename T, typename... Args> inline void rd(T &x, Args &...args) {
    rd(x);
    rd(args...);
}
template <typename T> inline void writeInt(T x, char space = '\n') {
    if (x < 0) {
        cout << "-";
        x = -x;
    }
    static int sta[41];
    int top = 0;
    do {
        sta[top++] = x % 10, x /= 10;
    } while (x);
    while (top) putchar(sta[--top] + 48);
    if (space) putchar(space);
}

template <typename T, typename... Args> inline void writeInt(T x, Args ...r) {
    writeInt(x, ' ');
    writeInt(r..., ' ');
    cout << endl;
}
template <typename T>
concept extended_integral = integral<T> or is_same_v<T, __int128>;
template <typename T> requires extended_integral<T> inline void writeVector(const vector<T>& x) {
    for (auto e : x) {
        writeInt(e, ' ');
    }
    cout << endl;
}
template <typename T> inline void writeVector(const vector<T>& x) {
    for (auto e : x) {
        cout << e << ' ';
    }
    cout << endl;
}
void yes() {
    cout << "Yes" << endl;
}
void no() {
    cout << "No" << endl;
}
// ----------------- Item Get Border Line! -----------------
#define MULTI
void Main() {
    int n, m, k;
    rd(n, m, k);
    
    vector<int> a(n + 12);
    a[n + 1] = -1;
    repn(i, n) rd(a[i]);
    set<int> s;
    repn(i, n) s.insert(a[i]);
    if (s.size() == 1) {
        cout << ceil(n /(double) k) << endl;
        return;
    }
    vector<int> blockSize;
    int cur = 0;
    repn(i, n + 1) {
        if (a[i] != a[i - 1] && i != 1) {
            blockSize.push_back(cur);
            cur = 1;
        } else {
            cur++;
        }
    }
    if (a[n] == a[1]) {
        auto b = blockSize.back();
        blockSize.pop_back();
        blockSize[0] += b;
    }
    int ans = 0;
    bool flag = false;
    for (auto x: blockSize) {
        if (x >= k) flag = true;
        ans += ceil(x / (double)k);
    }
    if (!flag) cout << -1 << endl;
    else cout << ans << endl;
}
    

int main() {
#ifdef MULTI
    int T;
    rd(T);
    while (T--)
#endif
        Main();
    return 0;
}