using System;

public class Program

{

    public static void Main(string[] args)

    {

        int indice = -1;

        int numPesquisar = 5;

        int[] a = new int[] {3, 7, 4, 9, 2, 6, 7, 8, 9, 2};

        for (int i = 0; i < a.Length; i++){

            if (a[i] == numPesquisar){

                indice = i;

                break;

            }

        }

        Console.WriteLine("Índice: {0}", indice);

    }

}