using System;

public class Program

{

    public static void Main()

    {

        int students_2=0;

        int students_1=0;

        int students_0=0;

        for(int i=1; i<=3; i++)  

        { Console.WriteLine("enter grade on assignment 1:");

         int grade1 = int.Parse(Console.ReadLine());

         Console.WriteLine("enter grade on assignment 2:");

         int grade2 = int.Parse(Console.ReadLine());

         if (grade1==-1 && grade2==-1)

         { students_1++;

         }

         else if(grade1==-1 || grade2==-1)

         { students_0++;

         }

         else

         { students_2++;

         }

        }

    }    

}

​