import datetime
tm1 = '1:51:01'
tm2 = '0:27:50'
to_seconds = lambda x: int(x.split(':')[2]) + int(x.split(':')[1]) * 60 + int(x.split(':')[0])* 60 * 60
date1 = datetime.datetime.strptime(tm1, '%H:%M:%S')
date2 = date1 + datetime.timedelta(seconds=to_seconds(tm2))
print(date2.strftime('%H:%M:%S'))
# 02:18:51