CODE EXAMPLE FOR PYTHON

codeforces 1133A in python

sh, sm = map(int, input().split(':')) # start time
eh, em = map(int, input().split(':')) # end time

mid_m = (((sh * 60) + sm) + ((eh * 60) + em)) // 2

if mid_m >= 1440:
    mid_m = mid_m - 1440
mh = mid_m // 60
mm = mid_m - (mh * 60)

if mh < 10:
    mh = '0' + str(mh)
if mm < 10:
    mm = '0' + str(mm)
print(mh, ':', mm, sep='')