parts = ["M1", "S2", "M1", "M1", "B3", "S2"]
limit = 2
answer = []
count = 1

parts.sort()
for i in range(len(parts)-1):
    if parts[i] == parts[i+1]:
        count += 1
        if count > limit:
            answer.append(parts[i])
    else:
        count = 1

print(answer)