Write a C# Sharp program to find out the sum of in A.P. series

using System;  
public class Exercise49
{  
    public static void Main()
     {

    int n1,df,n2,i,ln;
    int s1=0;
	
	Console.Write("\n\n");
    Console.Write("Find out the sum of in A.P. series:\n");
    Console.Write("-------------------------------------");
    Console.Write("\n\n");	


    Console.Write("Input  the starting number of the A.P. series: ");
    n1 = Convert.ToInt32(Console.ReadLine());	

    Console.Write("Input the number of items for  the A.P. series: ");
    n2 = Convert.ToInt32(Console.ReadLine());	

    Console.Write("Input  the common difference of A.P. series: ");
    df = Convert.ToInt32(Console.ReadLine());	

    s1 = ( n2 * ( 2 * n1 + ( n2 -1 ) * df ) )/ 2;
    ln = n1 + (n2-1) * df;
    Console.Write("\nThe Sum of the  A.P. series are : \n");

    for(i=n1;i<=ln; i= i + df ){
         if (i != ln)
             Console.Write("{0} + ",i);
         else
             Console.Write("{0} = {1} \n\n",i,s1);
    }
}
}