#include<bits/stdc++.h>
using namespace std;

#define int        long long int
#define pb         push_back
#define all(x)     x.begin(),x.end()
#define allr(x)    x.rbegin(),x.rend()
#define ii         pair<int,int>
#define endl       '\n'

void pipra(int tc) {
    int n, k, d;
    cin >> n >> k >> d;
    vector<int> a(n);
    for(int i = 0 ; i < n ; i++)
        cin >> a[i];
    int sum = accumulate(a.begin(), a.begin() + k, 0);
    // int cnt = count(a.begin(), a.begin() + k, 1);
    // cout << sum << ' ' << cnt << endl;
    int zero = -1;
    if(sum %d == 0) {
        if(sum == k) {
            cout << 1 << endl;
            return;
        }
        else
            zero = 1;
    }
    for(int i = k ; i < n ; i++) {
        sum += a[i] == 1;
        sum -= a[i - k] == 1;
        if(sum %d == 0) {
            if(sum == k) {
                cout << i - k + 2 << endl;
                return;
            }
            else if(zero == -1)
                zero = i - k + 2;
        }
    }
    cout << zero << endl;
}

int32_t main() {
    ios_base::sync_with_stdio(false);
    cin.tie(NULL); cout.tie(NULL);

    int t = 1;
    cin >> t;
    for(int i = 1 ; i <= t ; i++)
        pipra(i);
    return 0;
}