using System;

using System.Collections.Generic;

using System.Linq;

​

public class Program

{

    public static void Main()

    {

            int[] data = new int[] { -7, -5, -3, 1, 3, 6, 4, 1, 2 };         

            int[] newArray = new int[data.Max()];

​

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

            {

                if (data[i] > 0)

                {

                    newArray[data[i] - 1] = 1;

                }

            }

​

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

            {

                if (newArray[i] == 0)

                {

                    Console.WriteLine("First missing positive is " + (i + 1));

                    break;

                }

            }

    }

}