Code tham khảo:

def ktra(k):
	for i in range(0, n):
		while k[i] not in ('T', 'D', 'V', 'X'):
			print("Nhap lai mau son!")
			k = str(input())
		return True

n = int(input())
nha = []
if 1 <= n <= 2500:
	k = str(input())
	while not ktra(k):
		pass
	for m in range(1, n):
		nha.append(k[m])
	count = 0
	for i in range(1, len(nha) - 1):
		if nha[i] == nha[i + 1]:
			count = count + 1
	print(count)
else:
	print('Nhap lai so nha!')
#JACVII222