using static System.Console;

using System.Text;

​

public class Program {

    public static void Main() {

        var hs = "/4587 / 5458/";

        var texto = new StringBuilder(hs.Length);

        var digito = true;

        foreach (var chr in hs) {

            if (char.IsDigit(chr)) {

                if (!digito) texto.Append(';');

                texto.Append(chr);

                digito = true;

            } else digito = false;

        }

        WriteLine(texto.ToString());

    }

}