import sys input = sys.stdin.readline ans = 0 for i in range(int(input())): h, m = map(int, input().split(":")) ans += h * 60 + m d = (ans // 3600) h = (ans % 3600) // 60 m = ans % 60 print("{:02d}:{:02d}:{:02d}".format(d, h, m))