calculator.cs

using System;
using System.Collections.Generic;

namespace Demo {
  public class Calculator {
    private List<int>args = new List<int>();
  
    public void Push(int n) {
      args.Add(n);
    }
   
    public int Add() {
      int result = 0;
      foreach(int n in args) {
        result += n;
      }
      return result;
    }
  }
}