import java.util.*;
import java.util.stream.*;
 
public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        // 读取输入
        String[] nm = sc.nextLine().split(",");
        int n = Integer.parseInt(nm[0]);
        int m = Integer.parseInt(nm[1]);
        int[] hams = Arrays.stream(sc.nextLine().split(",")).mapToInt(Integer::parseInt).toArray();
        int[] costs = Arrays.stream(sc.nextLine().split(",")).mapToInt(Integer::parseInt).toArray();
        int k = Integer.parseInt(sc.nextLine());
 
        // 计算每秒法力恢复值
        int recover = Math.max(1, m / 10);
 
        // BFS队列：存储状态 [时间t, 当前法力currentM, Boss剩余血量currentK]
        Queue<int[]> queue = new LinkedList<>();
        queue.offer(new int[]{0, m, k});
        // 记录已访问的状态（避免重复计算）
        Set<String> visited = new HashSet<>();
        visited.add(m + "," + k);
 
        while (!queue.isEmpty()) {
            int[] curr = queue.poll();
            int t = curr[0];
            int currentM = curr[1];
            int currentK = curr[2];
 
            // 尝试释放每个技能
            for (int i = 0; i < n; i++) {
                int cost = costs[i];
                int harm = hams[i];
                if (currentM >= cost) {
                    int newK = currentK - harm;
                    // Boss血量≤0，击杀成功
                    if (newK <= 0) {
                        System.out.println(t + 1);
                        return;
                    }
                    // 修正：释放技能后先消耗法力，经过1秒后再恢复法力
                    // 先计算释放技能后的法力（不立即恢复）
                    int newMAfterCast = currentM - cost;
                    // 再计算1秒后的恢复（符合时间流逝逻辑）
                    int newM = newMAfterCast + recover;
                    newM = Math.min(newM, m); // 不超过最大法力
                    String key = newM + "," + newK;
                    if (!visited.contains(key)) {
                        visited.add(key);
                        queue.offer(new int[]{t + 1, newM, newK});
                    }
                }
            }
 
            // 尝试等待（耗时1秒，恢复法力）
            int newMWait = currentM + recover;
            newMWait = Math.min(newMWait, m);
            String keyWait = newMWait + "," + currentK;
            if (!visited.contains(keyWait)) {
                visited.add(keyWait);
                queue.offer(new int[]{t + 1, newMWait, currentK});
            }
        }
 
        // 无法击杀Boss
        System.out.println(-1);
    }
}
 

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2,25
10,15
10,15
25