array = []
for _ in range(4):
line = input().split(':')
for i in range(len(line)):
line[i] = int(line[i])
array.append(line)
for i in range(len(array)):
array[i] = array[i][0] * 60 + array[i][1]
n = (array[1] - array[0] + array[3] - array[2] + 1440 * (array[3] < array[0]) + 1) // 2
fisrt_num = '0' + str(n // 60) if len(str(n // 60)) == 1 else str(n // 60)
second_num = '0' + str(n % 60) if len(str(n % 60)) == 1 else str(n % 60)
print(f"{fisrt_num}:{second_num}")
t = [v[0] * 60 + v[1] for v in t]
t = (t[1] - t[0] + t[3] - t[2] + 1440 * (t[3] < t[0]) + 1) // 2
print('%02d:%02d' % (t // 60, t % 60))