using System;

public class Program

{

    public static void Main()

    {

        var solution = new Solution();

        var input1 = new string[] { "02:30", "04:35" };

        var input2 = new string[] { "11:00", "11:01" };

        Console.WriteLine(solution.ConvertTime(input1[0], input1[1]));

        Console.WriteLine(solution.ConvertTime(input2[0], input2[1]));

    }

}

​

public class Solution 

{

    public int ConvertTime(string current, string correct)

    {

        var minutesCurrent = GetMinutes(current);

        var minutesCorrect = GetMinutes(correct);

​

        int operations = 0;

        var diff = minutesCorrect - minutesCurrent;

        while (diff > 0)

        {

            if (diff >= 60)

            {

                minutesCurrent += 60;

                operations++;

            }

            else if (diff >= 15)

            {

                minutesCurrent += 15;

                operations++;

            }

            else if (diff >= 5)

            {

                minutesCurrent += 5;

                operations++;

            }

            else if (diff >= 1)

            {

                minutesCurrent += 1;

                operations++;

            }

​

            diff = minutesCorrect - minutesCurrent;

        }

​

        return operations;

    }

​

    private int GetMinutes(string input)

    {

        var minutes = (input[0] - 48) * 10 * 60;

        minutes += (input[1] - 48) * 60;

        minutes += (input[3] - 48) * 10;

        minutes += (input[4] - 48);

​

        return minutes;

    }

}