easy to proof : f(ab) = f(a)f(b)

Enumerating the ans for 1 digit is enough. Then we can deduct the answer for any length string!

import sys
from collections import defaultdict


def main():
    data = sys.stdin.read().split()
    # print(data)
    n = int(data[0])
    S = data[1]
    # print(S)
    code = {
        "2": "2",
        "3": "3",
        "4": "322",
        "5": "5",
        "6": "53",
        "7": "7",
        "8": "7222",
        "9": "7332",
    }
    ans = []
    for c in S:
        if c != "1" and c != "0":
            ans.append(code[c])
    # print(ans)
    ls = [c for c in "".join(ans)]
    # print(ls)
    ls.sort(reverse=True)
    print("".join(ls))


main()