RE 本地可以，线上就是不行

def add(n, m):
    last = {"A": 10, "B": 11, "C": 12, "D": 13, "E": 14, "F": 15}
    n = [(int(i) if (i not in "ABCDEF") else last[i]) for i in str(n)]
    n_ = n[::-1]

    for i in range(len(n)-1, -1, -1):
        x = n[i] + n_[i]
        y = x % m
        if y > 9:
            n[i] = chr(65 + y - 10)

        else:
            n[i] = y

        if x//m > 0:
            if i == 0:
                n.insert(0, x//m)

            else:
                n[i-1] += x//m

    return "".join(map(str, n))

m = int(input())
n = input()

i = 1
while i <= 30:
    n = add(n, m)
    if n == n[::-1]:
        print(f"STEP={i}")
        break

    i += 1

else:
    print("Impossible!")