class OrdinalNumbers:
    def __init__(self, n):
        self.n = n
        
    def solution(self):
        t = int(str(self.n)[-1])-1
        return str(self.n)+ ("th" if ((self.n>10) and (self.n<20)) else (["st", "nd", "rd"][t:t+1] or ["th"])[0])

from typing import Sequence, Optional

def missing_integer(sequence: Sequence[int]) -> Optional[int]:
    return next((i + sequence[0] for i, num in enumerate(sequence) if num != i + sequence[0]), None)

describeAge=a=>`You're a(n) ${["kid","teenager","adult","elderly"][(a>=13)+(a>=18)+(a>=65)]}`;