from typing import List
from typing import Union


def perfect_score(student_info: List[List[Union[str, int]]]) -> Union[List[Union[str, int]], str]:
    """
    :param student_info: list of [<student name>, <score>] lists
    :return: First [<student name>, 100] found OR "No perfect score."
    """
    for elem in student_info:
        if elem[1] == 100:
            return elem

    return "No perfect score."