def dfs(i, s):
    n = len(s)
    res = []
    while i < n and s[i] != ']':
        if s[i].isdigit():
            j = i
            while s[j].isdigit():
                j += 1
            k = int(s[i:j])
            i, l = self.dfs(j + 1, s)
            res += l * k
        else:
            res.append(s[i])
        i += 1
    return i, res

class Solution:
    def decodeString(self, s: str) -> str:
        res = []
        n = len(s)
        i = 0
        while i < n:
            i, l = dfs(i, s)
            res += l
        return ''.join(res)