You must put them in an array - and since you know how many elements you will have in the array - the calculation should be easy! You should only parse the numerical value.

Here it is:

using System;
 
class SumOfFiveNumbers
{
    static void Main()
    {
        string[] numbers = Console.ReadLine().Split(' ');
        decimal a = decimal.Parse(numbers[0]);
        decimal b = decimal.Parse(numbers[1]);
        decimal c = decimal.Parse(numbers[2]);
        decimal d = decimal.Parse(numbers[3]);
        decimal e = decimal.Parse(numbers[4]);
         
        Console.WriteLine(a+b+c+d+e);
    }
}