Plus 15 minutes

using System;

namespace TimePlus15
{
    class Program
    {
        static void Main(string[] args)
        {
            var hours = int.Parse(Console.ReadLine());
            var minutes = int.Parse(Console.ReadLine());

            if (minutes + 15 > 59)
            {
                hours += 1;
                minutes = 15 - (60 - minutes);
            }
            else if(minutes + 15 <= 59) minutes += 15;

            if (hours == 24) hours = 0;

            Console.WriteLine("{0}:{1:00}", hours, minutes);
        }
    }
}