Sum of All Alternative Numbers

using System;
using System.Collections.Generic;
using System.Text;

namespace sum_of_alternative_numbers
{
class alternat
{
static void Main(string[] args)
{
int[] a = new int[20];
int i,sum = 0,n;
Console.WriteLine("\tSUM OF ALTERNATIVE NUMBERS");
Console.WriteLine("\t***************************");
Console.WriteLine("Enter The Array Limit");
n = int.Parse(Console.ReadLine());
Console.WriteLine("Enter the Elements One By One");
for (i = 1; i <= n; i++)
{
a[i] = int.Parse(Console.ReadLine());
}
Console.WriteLine("The Alternative Numbers Are");
for (i = 1; i <= n; i = i + 2)
{
Console.WriteLine("{0}", a[i]);
sum = sum + a[i];
}
Console.WriteLine("The Sum of Alternative Numbers={0}", sum);


}
}
}