using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace ConsoleApp5 {
    class Program {
        static void Main(string[] args) {
            TimeSpan begin = new TimeSpan(8, 0, 0);
            TimeSpan end = new TimeSpan(18, 0, 0);
            TimeSpan[] startTimes = new TimeSpan[] {
                new TimeSpan(10, 0, 0),
                new TimeSpan(12, 0, 0)
            };
            int[] durations = new int[] {
                60, 120
            };
            var a = Average(startTimes, durations, begin, end, 30);
            foreach (var b in a)
                Console.WriteLine(b);
        }

        static string[] Average(TimeSpan[] startTimes, int[] durations, TimeSpan beginWorkingTime, TimeSpan endWorkingTime, int consultation) {
            List<TimeSpan> lst = new List<TimeSpan>();
            TimeSpan current = Copy(beginWorkingTime);
            for (int i = 0; i < durations.Length; ++ i) {
                while (current + new TimeSpan(0, consultation, 0) <= startTimes[i]) {
                    lst.Add(Copy(current));
                    current += new TimeSpan(0, consultation, 0);
                }
                current = startTimes[i] + new TimeSpan(0, durations[0], 0);
            }
            while (current + new TimeSpan(0, consultation, 0) <= endWorkingTime) {
                lst.Add(Copy(current));
                current += new TimeSpan(0, consultation, 0);
            }
            List<string> ret = new List<string>();
            foreach (var a in lst) {
                TimeSpan p = a + new TimeSpan(0, consultation, 0);
                DateTime x = new DateTime(1970, 1, 1, a.Hours, a.Minutes, a.Seconds);
                DateTime y = new DateTime(1970, 1, 1, p.Hours, p.Minutes, p.Seconds);
                ret.Add($"{x.ToString("HH:mm")}-{y.ToString("HH:mm")}");
            }
            return ret.ToArray();
        }

        static TimeSpan Copy(TimeSpan time) {
            return new TimeSpan(time.Hours, time.Minutes, time.Seconds);
        }
    }
}