#include <bits/stdc++.h>
using namespace std;
int nships(int a, int b, int l) {
  int n = b - a - 1, ret;
  ret = n / (l + 1);
  if (n % (l + 1) == l) ret++;
  return ret;
}
int main() {
  ios::sync_with_stdio(false);
  cin.tie(0);
  int n, k, a, m, x;
  cin >> n >> k >> a >> m;
  set<int> st;
  set<int>::iterator it1, it2;
  st.insert(0);
  st.insert(n + 1);
  int curr = nships(0, n + 1, a);
  for (int i = 1; i <= m; ++i) {
    cin >> x;
    it1 = st.lower_bound(x);
    it2 = it1;
    it1--;
    curr -= nships(*it1, *it2, a);
    curr += nships(*it1, x, a);
    curr += nships(x, *it2, a);
    if (curr < k) {
      cout << i;
      return 0;
    }
    st.insert(x);
  }
  cout << -1;
}
