#include <bits/stdc++.h>
using namespace std;
const int N = 2000005;
int n, k, a, m;
int p[N];
int b[N];
bool check(int mid) {
  for (int i = 1; i <= mid + 1; i++) {
    b[i] = p[i - 1];
  }
  sort(b + 1, b + mid + 2);
  b[0] = 0;
  b[mid + 2] = n + 1;
  int ans = 0;
  for (int i = 1; i <= mid + 2; i++) {
    ans += (b[i] - b[i - 1]) / (a + 1);
  }
  return ans >= k;
}
int solve() {
  int l = 0;
  int r = m;
  while (l < r) {
    int mid = (l + r) >> 1;
    if (check(mid)) {
      l = mid + 1;
    } else {
      r = mid;
    }
  }
  if (l == m)
    return -1;
  else
    return l + 1;
}
int main() {
  ios::sync_with_stdio(false);
  cin >> n >> k >> a >> m;
  for (int i = 0; i < m; ++i) cin >> p[i];
  cout << solve() << endl;
  return 0;
}
