Take the input values ββin an integer list or array, then use the following code
List<int> intlist=new List<int>();
intlist.Add(2);
intlist.Add(3);
..
..
var average= intlist.Average();
Using Average will calculate the average of the sequence of all integers in the list.
UPDATE : or if the point is to use integers, then you need to use the following code (don't forget to check the entries readline())
public decimal Average()
{
int value = 0;
for(int i=0;i<5;i++)
{
value+=ConvertToInt32(Console.ReadLine());
}
return value/5;
}