Getting a time limit exceeds error on test #7. Help and understanding of efficient solution would be well appreciated.

n = int(input())
string = ''
group_count = 0
for i in range(n):
    num = input()

    if i == 0 or num[0] == string[-1]:
        string += num     
        group_count += 1
    else:
        string += num

print(group_count)