Can't add script bacause of class cannot be found

What should I do?

using UnityEngine;
using System.Collections.Generic;

public class NewBehaviourScript : MonoBehaviour {
    // Изменение скорости перемещения героя
    public float playerSpeed = 2.0f;

    // Текущая скорость перемещения
    private float currentSpeed = 0.0f;

    // Создание переменных для кнопок
    public List<KeyCode> upButton;
    public List<KeyCode> downButton;
    public List<KeyCode> leftButton;
    public List<KeyCode> rightButton;

    // Сохранение последнего перемещения
    private Vector3 lastMovement = new Vector3();

	
	// Update is called once per frame
	void Update () {
		
	}
}

If the script compiles correct, make sure the file is named after the class (NewBehaviourScript.cs)

Don’t use space between words in the script name. Type it without space :NewBehaviourScript