数字到单词的转换，印度货币格式，按键时最多16位数字

def convert_to_words(num):
    units = ["", "One", "Two", "Three", "Four", "Five", "Six", "Seven", "Eight", "Nine", "Ten", "Eleven", "Twelve", "Thirteen", "Fourteen", "Fifteen", "Sixteen", "Seventeen", "Eighteen", "Nineteen"]
    tens = ["", "", "Twenty", "Thirty", "Forty", "Fifty", "Sixty", "Seventy", "Eighty", "Ninety"]
    if num < 20:
        return units[num]
    if num < 100:
        return tens[num // 10] + " " + units[num % 10]
    if num < 1000:
        return units[num // 100] + " Hundred " + convert_to_words(num % 100)
    if num < 100000:
        return convert_to_words(num // 1000) + " Thousand " + convert_to_words(num % 1000)
    if num < 10000000:
        return convert_to_words(num // 100000) + " Lakh " + convert_to_words(num % 100000)
    return convert_to_words(num // 10000000) + " Crore " + convert_to_words(num % 10000000)

def convert_to_words(num):
    if num < 0 or num > 9999999999999999:
        return "Invalid input"
    # 转换逻辑...