using System;

​

public class Program

{

    public static void Main()

    {

          Console.WriteLine(isSystematicallyIncreasing(new int[]{1, 1, 2, 1, 2, 3, 1, 2, 3, 4, 1, 2, 3, 4, 5, 1, 2, 3, 4, 5, 6}));

​

    }

    static int isSystematicallyIncreasing(int[] a)

    {

        int preNum = 1;

        for(int i = 0; i < a.Length; i++)

        {

            if(i == 0 || i == 1)

            {

                if(a[i] != 1)

                    return 0;

            }

            if(a[i] == 1 && i > 1)

            {

                if(a[i -1] != preNum + 1)

                    return 0;

                preNum = a[i -1 ];

            }

            if((a[i] != 1 && a[i] != a[i - 1] + 1) || a[i] > preNum +1)

                return 0;

        }

      return 1;

​

    }

​

​

}