#include <bits/stdc++.h>
using namespace std;
int main() {
  int x, m, n, k, a;
  cin >> n >> k >> a >> m;
  a++;
  set<int> s;
  s.insert(0);
  s.insert(n + 1);
  int sz = (n + 1) / a;
  for (int i = 0; i < m; i++) {
    if (sz < k) {
      cout << i << endl;
      return 0;
    }
    scanf("%d", &x);
    set<int>::iterator it = s.lower_bound(x);
    int c = *it--;
    int v = (c - *it) / a;
    it++;
    c = *it--;
    int b = (c - x) / a + (x - *it) / a;
    s.insert(x);
    sz -= v - b;
  }
  if (sz < k)
    cout << m;
  else
    cout << "-1\n";
}
