Chinese clock

n = int(input())
M = 60 * 60 * 12
cnt = [0] * M
for i in range(n):
  h, m, s = map(int, input().split(':'))
  cnt[(h - 1) * 3600 + m * 60 + s] += 1

times = []
for i in range(M):
  times += [i] * cnt[i]

for i in range(n):
  times.append(times[i] + M)

prev_sum = 0
for i in range(1, n):
  prev_sum += (times[i] - times[i-1]) * i

j = n - 1
mins = prev_sum
for i in range(n, 2*n-1):
  prev_sum += (times[i] - times[i-1]) * (n-1) - (times[i-1] - times[i-n])
  if prev_sum < mins or prev_sum == mins and j == n - 1:
    mins = prev_sum
    j = i - n
ans = times[j]
print("%d:%02d:%02d" % (ans // 3600 + 1, ans % 3600 // 60, ans % 60 ))