def common_chars(a: str, b: str) -> int:
    cc1 = a.lower()
    cc2 = b.lower()
    valores = []

    for x in range(len(cc1)):
        for y in range(len(cc2)):
            if cc1[x] == cc2[y] and cc1[x] not in valores:
                valores.append(cc1[x])
    return len(valores)