using System;
public class Program
{
public static void Main()
Int32 a,b,c;
String textik;
do
Console.WriteLine("Zadej stranu a : ");
textik = Console.ReadLine();
a = Convert.ToInt32(textik);
if (a==0)
Console.WriteLine("Stana 'a' se nesmí rovnat nule...");
} while(a==0);
}