func fish(a, b []int) int {
	size := len(a)
	dead := 0
	downstream := make([]int, 0, size)

	for i := 0; i < size; i++ {
		if b[i] == 1 {
			downstream = append(downstream, a[i])
		} else {
			for len(downstream) > 0 {
				dead++
				if a[i] > downstream[len(downstream)-1] {
					downstream = downstream[:len(downstream)-1]
				} else {
					break
				}
			}
		}
	}

	return size - dead
}