import java.util.*;

public class Main {
	public static void main (String[] args) {
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		int[] toys = new int[n];
		for (int i = 0; i < n; i++) {
		    toys[i] = sc.nextInt();
		}
		Arrays.sort(toys);
		int m = sc.nextInt();
		int[] boxes = new int[m];
		for (int i = 0; i < m; i++) {
		    boxes[i] = sc.nextInt();
		}
		Arrays.sort(boxes);
		int right = m - 1;
		TreeMap<Integer, Integer> using = new TreeMap<>();
		using.put(Integer.MAX_VALUE, 0);
		for (int i = n - 1; i >= 0; i--) {
		    int key = using.ceilingKey(toys[i]);
		    if (key == Integer.MAX_VALUE) {
		        if (right < 0 || boxes[right] < toys[i]) {
		            System.out.println(-1);
		            return;
		        }
		        using.put(boxes[right] - toys[i], using.getOrDefault(boxes[right] - toys[i], 0) + 1);
		        right--;
		    } else {
		        if (using.get(key) == 1) {
		            using.remove(key);
		        } else {
		            using.put(key, using.get(key) - 1);
		        }
	            using.put(key - toys[i], using.getOrDefault(key - toys[i], 0) + 1);
		    }
		}
		System.out.println(m - right - 1);
	}
}