import java.util.*;

public class Main
{
    public static void main(String[] args)
    {
        Scanner sc = new Scanner(System.in);
        final int n = sc.nextInt();
        final int m = sc.nextInt();
        int lMax = Integer.MIN_VALUE;
        int rMin = Integer.MAX_VALUE;

        for (int i = 0;i<m;++i)
        {
            int l = sc.nextInt();
            int r = sc.nextInt();
            if (lMax < l) lMax = l;
            if (rMin > r) rMin = r;
        }

        int count = 0;
        for (int i = 0;i<=n;++i) if (lMax <= i && rMin >= i) ++count;

        System.out.println(count);
        sc.close();
    }
}
/tmp/hf-datasets-cache/medium/datasets/42704881117311-config-parquet-and-info-qiankunmu-Project_CodeNet-896c9d36/hub/datasets--qiankunmu--Project_CodeNet_Python800_and_Java250/snapshots/c899fde44a77ba1cc14973ed3de064e4ff3aadc7/Project_CodeNet_Java250.tar.gz