from typing import Tuple


def get_first_string(expression: str) -> Tuple[str, str]:
    """
    Reads the letter string in the beginning of the expression string.

    :param expression: str of the expression

    :return: letter string in the beginning and the string of the remaining
             expression
    """
    found_string = ''
    for char in expression:
        if char.isalpha():
            found_string += char
        else:
            break

    return found_string, expression[len(found_string):]