Error: "The namespace '<global namespace>' already contains a definition for 'GenerateChunk'

Question

I am following a tutorial on YouTube for how to make a Minecraft-like 2D game in Unity. Here's the link: https://www.youtube.com/watch?v=4ubrvkefphI&list=PL37wmdqtgqTIfYtBtAOZNUFR7BeE1XUGi&index=3
I have to scripts to generate the chunks of the world, "GenerateChunk" and "GenerateChunks" (notice the s on the end). This is the scripts:

GenerateChunk:

using UnityEngine;
using System.Collections;

public class GenerateChunk : MonoBehaviour {

public GameObject DirtTile;
public GameObject GrassTile;
public GameObject StoneTile;

public int width;
public float heightMultiplier;
public int heightAddition;

public float smoothness;

[HideInInspector]
public float seed;

void Start () {
    Generate ();
    seed = Random.Range (-10000, 10000);
}

public void Generate () {
    for (int i = 0; i < width; i++){
        int h = Mathf.RoundToInt (Mathf.PerlinNoise (seed, (i + transform.position.x) / smoothness) * heightMultiplier) + heightAddition;
        for (int j = 0; j < h; j++){
            GameObject selectedTile;
            if (j < h - 4) {
                selectedTile = StoneTile; 
            } else if (j < h - 1 ){
                selectedTile = DirtTile;
            } else {
                selectedTile = GrassTile;
            }

            GameObject newTile = Instantiate (selectedTile, Vector3.zero, Quaternion.identity) as GameObject;
            newTile.transform.parent = this.GameObject.transform;
            newTile.transform.localPosition = new Vector3 (i, j);
        }
    }
}

}

GenerateChunks:

using UnityEngine;
using System.Collections;

public class GenerateChunks : MonoBehaviour {

public GameObject chunk;
int chunkWidth;
public int numChunks;
float seed;

void Start () {
    chunkWidth = chunk.GetComponent<GenerateChunk> ().width;
    seed = Random.Range (-100000f, 100000f);
    Generate ();
}

public void Generate () {
    int lastX = -chunkWidth;
    for (int i = 0; i < numChunks; i++) {
        GameObject newChunk = Instantiate(chunk, new Vector3(lastX + chunkWidth, 0f), Quaternion.identity) as GameObject;
        newChunk.GetComponent<GenerateChunk> ().seed = seed;
        lastX += chunkWidth;
    }
}

}

Please help me!