example.py

import sys
from itertools import product

def solve():
    # Fast Read
    val = sys.stdin.read().strip()
    
    if not val:
        print("[]")
        return

    mapping = {
        "2": "abc", "3": "def", "4": "ghi", "5": "jkl",
        "6": "mno", "7": "pqrs", "8": "tuv", "9": "wxyz"
    }

    # 1. Collect the letter groups corresponding to digits
    # If val is "23", groups will be ["abc", "def"]
    groups = [mapping[d] for d in val if d in mapping]

    # 2. Use Cartesian Product (The "C-speed" optimization)
    # *groups unpacks the list so product receives ("abc", "def")
    result = [''.join(combo) for combo in product(*groups)]
    
    # The image shows printing the list format
    print(result)

if __name__ == "__main__":
    solve()