using System;

public class Program

{

    public static void Main(string[] args){

        int nb=0;

        string st="";

        do{

            try{

            Console.WriteLine("un nombre svp: ");

            st = Console.ReadLine();

            nb = Convert.ToInt32(st);

    }//try

        catch (FormatException e){

        Console.WriteLine("Valeur erronnée");

        }

        }while(nb==0);

    }

}