#include <bits/stdc++.h>
using namespace std;
const double eps = 1e-9;
const int inf = 20000;
const long long infLL = 9000000000000000000;
template <typename first, typename second>
ostream& operator<<(ostream& os, const pair<first, second>& p) {
  return os << "(" << p.first << ", " << p.second << ")";
}
template <typename T>
ostream& operator<<(ostream& os, const vector<T>& v) {
  os << "{";
  for (auto it = v.begin(); it != v.end(); ++it) {
    if (it != v.begin()) os << ", ";
    os << *it;
  }
  return os << "}";
}
template <typename T>
ostream& operator<<(ostream& os, const set<T>& v) {
  os << "[";
  for (auto it = v.begin(); it != v.end(); ++it) {
    if (it != v.begin()) os << ",";
    os << *it;
  }
  return os << "]";
}
template <typename T>
ostream& operator<<(ostream& os, const multiset<T>& v) {
  os << "[";
  for (auto it = v.begin(); it != v.end(); ++it) {
    if (it != v.begin()) os << ", ";
    os << *it;
  }
  return os << "]";
}
template <typename first, typename second>
ostream& operator<<(ostream& os, const map<first, second>& v) {
  os << "[";
  for (auto it = v.begin(); it != v.end(); ++it) {
    if (it != v.begin()) os << ", ";
    os << it->first << " = " << it->second;
  }
  return os << "]";
}
void faltu() { cerr << '\n'; }
template <typename T>
void faltu(T a[], int n) {
  for (int i = 0; i < n; ++i) cerr << a[i] << ' ';
  cerr << '\n';
}
template <typename T, typename... hello>
void faltu(T arg, const hello&... rest) {
  cerr << arg << ' ';
  faltu(rest...);
}
const int mx = 1e5 + 5;
long long a, b, h, w, n;
int arr[mx];
long long dp[mx][50];
int lim = 50;
long long a1, a2, b1, b2;
long long recur(long long cur, int pos, long long prod) {
  if (cur >= a1 && (prod / (cur / b1)) * b2 >= a2) return 0;
  if (cur >= a1) {
    long long temp = (prod / (cur / b1)) * b2;
    int cnt = 0;
    for (int i = pos; i < n; ++i) {
      ++cnt;
      temp *= arr[i];
      if (temp >= a2) break;
    }
    if (temp >= a2) return cnt;
    return inf;
  }
  if (pos == n) return inf;
  if (dp[cur][pos] != -1) return dp[cur][pos];
  int ret1 = inf, ret2 = inf;
  ret1 = recur(cur * arr[pos], pos + 1, prod * arr[pos]);
  if ((prod / (cur / b1)) * b2 < a2)
    ret2 = recur(cur, pos + 1, prod * arr[pos]);
  int ret = min(ret1, ret2) + 1;
  dp[cur][pos] = ret;
  return ret;
}
int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  ;
  cin >> a >> b >> h >> w >> n;
  for (int i = 0; i < n; ++i) cin >> arr[i];
  sort(arr, arr + n, greater<int>());
  memset(dp, -1, sizeof(dp));
  a1 = a, a2 = b, b1 = h, b2 = w;
  long long ans = recur(b1, 0, 1);
  memset(dp, -1, sizeof(dp));
  a1 = a, a2 = b, b1 = w, b2 = h;
  ans = min(ans, recur(b1, 0, 1));
  if (ans >= inf) ans = -1;
  cout << ans << '\n';
}
