using System;
using System.Collections;
using System.Collections.Generic;
using System.IO;
using System.Linq;

namespace D20._2
{
    public class R : StreamReader, IEnumerable
    {
        public R(Stream stream) : base(stream) { }
        public IEnumerator GetEnumerator()
        {
            while (true)
            {
                var line = ReadLine();
                if (line == null) break;
                yield return line;
            }
        }
    }
    class Program
    {
        static void Main(string[] args)
        {
            var ranges = new List<(uint start, uint end)>();
            ParseFile(args, ranges);

            ranges.Sort();

            ReduceRanges(ranges);

            uint count = 0;
            for (var i = 1; i < ranges.Count; ++i)
            {
                var r1 = ranges[i - 1];
                var r2 = ranges[i];

                count += r2.start - r1.end - 1;
            }

            Console.WriteLine($"The answer is : {count}");
        }

        private static void ReduceRanges(List<(uint start, uint end)> ranges)
        {
            for (var i = 1; i < ranges.Count; ++i)
            {
                var r1 = ranges[i - 1];
                var r2 = ranges[i];

                if (r2.start >= r1.start && r2.end <= r1.end)
                {
                    ranges.RemoveAt(i);
                    i--;
                    continue;
                }

                if (r2.start >= r1.start && r2.start <= r1.end + 1 && r2.end > r1.end)
                {
                    ranges[i] = (r1.start, r2.end);
                    ranges.RemoveAt(i - 1);
                    i--;
                    continue;
                }
            }
        }

        private static void ParseFile(string[] args, List<(uint start, uint end)> ranges)
        {
            using (var file = new R(File.OpenText(args[0]).BaseStream))
            {
                foreach (string line in file)
                {
                    var lr = line.Split("-");
                    var start = uint.Parse(lr[0]);
                    var end = uint.Parse(lr[1]);

                    ranges.Add((start, end));
                }
            }
        }
    }
}