c# move with arrow keys

//When you are using this code make sure it is for unity :) also make sure to 
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public class PlayerMovement : MonoBehaviour {

	// This is a reference to the Rigidbody component called "rb"
	public Rigidbody rb;

	public float forwardAndBackForce = 500f;	// Variable that determines the forward force
 	public float sidewaysForce = 500f;  // Variable that determines the sideways force

  	// We marked this as "Fixed"Update because we
	// are using it to mess with physics.
	void FixedUpdate ()
	{
		if (Input.GetKey("d"))	// If the player is pressing the "d" key
		{
			// Add a force to the right
			rb.AddForce(sidewaysForce  * Time.deltaTime, 0, 0);
		}

		if (Input.GetKey("a"))  // If the player is pressing the "a" key
		{
			// Add a force to the left
			rb.AddForce(-sidewaysForce * Time.deltaTime, 0, 0);
		}
		if (Input.GetKey("w"))  // If the player is pressing the "w" key
		{
			// Add a force to the Forward
			rb.AddForce(0, 0, forwardForce * Time.deltaTime);
		}
		if (Input.GetKey("s"))  // If the player is pressing the "s" key
		{
			// Add a force to the back
			rb.AddForce( 0, 0, -forwardForce * Time.deltaTime);
		}
	}
}