арифметика

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

class MainClass
{
  public static void Main (string[] args)
  {
    string chislo = @"(([1-9])\d*)";
    string pattern = $"({chislo}[-*+/])";
    string all_pattern = $"{pattern}*{chislo}";
    string str = Console.ReadLine();

    while(true)
    {
       foreach (Match match in Regex.Matches(str, all_pattern))
         Console.WriteLine(match.Value);

      str = Console.ReadLine();
       if (String.IsNullOrEmpty(str))
          break;
    }
  }
}