def to_snake_case(input_string):
    """
    Converts a string into a snake case.
    :param input_string: Input string
    :return: Snake case string
    :rtype: str
    """
    final = ''
    for item in input_string:
        if item.isupper():
            final += "_"+item.lower()
        else:
            final += item
    if final[0] == "_":
        final = final[1:]
    return final