zfill版本（80分）

import math

s, v = input().split()
v = int(v)
s = int(s)
time = math.ceil(s / v) + 10
remain = 480 + 24 * 60 - time
if remain >= 24 * 60:
    remain -= 24 * 60
end = str(remain % 60)
front = str(remain // 60)
s_f = front + ":" + end
print(s_f.zfill(5))

% format版本（AC）

import math

s, v = input().split()
v = int(v)
s = int(s)
time = math.ceil(s / v) + 10
remain = 480 + 24 * 60 - time
if remain >= 24 * 60:
    remain -= 24 * 60
end = remain % 60
front = remain // 60
print("%2d:%2d".(front,end))