#include <bits/stdc++.h>
using namespace std;
long long n, k, a, m;
long long arr[200005];
void need_for_speed() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  cout.tie(NULL);
}
bool isPossible(long long p) {
  vector<long long> v(p + 2);
  v[0] = 0;
  for (long long i = 1; i <= p; i++) v[i] = arr[i - 1];
  v[p + 1] = n + 1;
  long long cnt = 0;
  sort(v.begin(), v.end());
  for (long long i = 1; i <= p + 1; i++) {
    long long x = (v[i] - v[i - 1]) / (a + 1);
    cnt += x;
  }
  if (cnt >= k) return true;
  return false;
}
int32_t main() {
  need_for_speed();
  cin >> n >> k >> a;
  cin >> m;
  for (long long i = 0; i < m; i++) cin >> arr[i];
  if (isPossible(m)) {
    cout << -1 << endl;
    return 0;
  }
  long long s = 0, e = m;
  long long ans = -1;
  while (s <= e) {
    long long mid = (s + e) / 2;
    if (isPossible(mid)) {
      s = mid + 1;
    } else {
      ans = mid;
      e = mid - 1;
    }
  }
  cout << ans << endl;
}
