#include <bits/stdc++.h>
using namespace std;
struct data {
  int x, id;
} x[200010];
int n, k, a, m;
inline int read() {
  int s = 0, w = 1;
  char c = getchar();
  for (; !isdigit(c); c = getchar())
    if (c == '-') w = -1;
  for (; isdigit(c); c = getchar()) s = (s << 1) + (s << 3) + (c ^ 48);
  return s * w;
}
bool cmp(data x, data y) { return x.x < y.x; }
bool check(int mid) {
  int cnt = 0, l = 0;
  for (int i = 1; i <= m; ++i)
    if (x[i].id <= mid) cnt += (x[i].x - l) / (a + 1), l = x[i].x;
  cnt += (n - l + 1) / (a + 1);
  return cnt < k;
}
int main() {
  n = read(), k = read(), a = read(), m = read();
  for (int i = 1; i <= m; ++i) x[i] = (data){read(), i};
  sort(x + 1, x + 1 + m, cmp);
  int l = 1, r = m, ans = -1;
  while (l <= r) {
    int mid = (l + r) >> 1;
    if (check(mid))
      ans = mid, r = mid - 1;
    else
      l = mid + 1;
  }
  printf("%d\n", ans);
  return 0;
}
