def uncommonChars(s1, s2):
    #code here
    freq1 = [False] * 26
    freq2 = [False] * 26

    # Marcar caracteres presentes en s1
    for c in s1:
        freq1[ord(c) - ord('a')] = True

    # Marcar caracteres presentes en s2
    for c in s2:
        freq2[ord(c) - ord('a')] = True

    result = ""

    # Recorrer el alfabeto
    for i in range(26):
        if freq1[i] != freq2[i]:
            result += chr(i + ord('a'))

    return result

print(uncommonChars("geeksforgeeks", "geeksquiz"))