题解 | #小欧的选数乘积#

import java.io.*;
import java.util.*;
import java.math.BigInteger;

public class Main {
    static void solve() {
        long x = in.nextLong(), y = in.nextLong();
        int n = in.nextInt();
        TreeSet<Integer> set = new TreeSet<>(Comparator.reverseOrder());
        for(int i=1;i<=n;i++) {
            int z = in.nextInt();
            set.add(z);
        }
        if(x>=y) {
            out.println(0);
            return;
        }
        int ans=0;
        for(int v:set) {
            x*=v;
            ans++;
            if(x>=y) {
                out.println(ans);
                return;
            }
        }
        out.println(-1);
    }


    public static void main(String[] args) {
        solve();
        out.flush();
    }

    static FastReader in = new FastReader();
    static PrintWriter out = new PrintWriter(System.out);

    static class FastReader {
        static BufferedReader br;
        static StringTokenizer st;

        FastReader() {
            br = new BufferedReader(new InputStreamReader(System.in));
        }

        String next() {
            String str = "";
            while (st == null || !st.hasMoreElements()) {
                try {
                    str = br.readLine();
                } catch (IOException e) {
                    throw new RuntimeException(e);
                }
                st = new StringTokenizer(str);
            }
            return st.nextToken();
        }

        int nextInt() {
            return Integer.parseInt(next());
        }

        double nextDouble() {
            return Double.parseDouble(next());
        }

        long nextLong() {
            return Long.parseLong(next());
        }
    }
}