// C# program to the nth prime number

using System;

using System.Collections;

​

public class Program_13

{

// initializing the max value

static int MAX_SIZE = 1000005;

​

// To store all prime numbers

static ArrayList primes = new ArrayList();

​

// Function to generate N prime numbers using

// Sieve of Eratosthenes

static void SieveOfEratosthenes()

{

    // Create a boolean array "IsPrime[0..MAX_SIZE]"

    // and initialize all entries it as true.

    // A value in IsPrime[i] will finally be false

    // if i is Not a IsPrime, else true.

    bool [] IsPrime = new bool[MAX_SIZE];

    for(int i = 0; i < MAX_SIZE; i++)

        IsPrime[i] = true;

    for (int p = 2; p * p < MAX_SIZE; p++)

    {

        // If IsPrime[p] is not changed,

        // then it is a prime

        if (IsPrime[p] == true)

        {

            // Update all multiples of p greater than or

            // equal to the square of it

            // numbers which are multiple of p and are

            // less than p^2 are already been marked.

            for (int i = p * p; i < MAX_SIZE; i += p)

                IsPrime[i] = false;

        }

    }

​

    // Store all prime numbers

    for (int p = 2; p < MAX_SIZE; p++)

    if (IsPrime[p] == true)

            primes.Add(p);

}

​

// Driver Code

public static void Main ()

{

    // Function call

    SieveOfEratosthenes();

    Console.WriteLine("ENTER NUM");

    int number = Convert.ToInt32(Console.ReadLine());

​

    Console.WriteLine(" prime number is " +

                                primes[number-1]);

​

}

}

​

// This code is contributed by ihritik

​