names = ["alice", "bob", "charlie", "david", "ellen"]
target = "david"

left = 0
right = len(names) - 1
answer = -1

while left <= right:
    mid = (left + right) // 2

    if names[mid] == target:
        answer = mid
        break
    elif names[mid] < target:
        left = mid + 1
    else:
        right = mid - 1

print(answer)