#include <bits/stdc++.h>
using namespace std;
int a, b, h, w, n, m, i, d[100179];
void z(int64_t aa, int64_t bb, int x, int s) {
  if (aa >= a && bb >= b) {
    m = min(m, n - x);
    return;
  }
  if (!x) return;
  s == 1 && d[x] == 2 ? s = 2 : 0;
  s == 2 && aa >= a ? s = 0 : 0;
  if (s > 0 && aa < a) z(aa * d[x], bb, x - 1, s);
  if (s < 2 && bb < b) z(aa, bb * d[x], x - 1, s);
}
int main() {
  cin >> a >> b >> h >> w >> n;
  for (; i < n; i++) cin >> d[i + 1];
  sort(d + 1, d + n + 1);
  m = n + 1;
  z(h, w, n, 1);
  z(w, h, n, 1);
  cout << (m > n ? -1 : m);
}
