unityscript - C# not running in Unity? (Basic) -

so, i'm playing around c# code in unity first time. i'm creating little script dink around with, not actual use. error get. (only assignment, call, increment, decrement, , new object expressions can used statement)

using unityengine; using system.collections;  public class movement : monobehaviour {      public int speed = 10;     public int money = 10;     // use initialization     void start () {      }      // update called once per frame     void update () {         if(input.getkey(keycode.w)) {             transform.translate (vector3.forward * speed * time.deltatime);         }         if(input.getkey(keycode.a)) {             transform.translate (vector3.left * speed * time.deltatime);         }         if(input.getkey(keycode.s)) {             transform.translate (vector3.back * speed * time.deltatime);         }         if(input.getkey(keycode.d)) {             transform.translate (vector3.right * speed * time.deltatime);         }         if(input.getkey(keycode.return && money >= 10)) {             debug.log("you bought sword!");             money - 10;         } else {             debug.log("you don't have enough money!");         }     } } 

the error in title. won't let me run it. know did wrong? : )

it looks want

money -= 10; 

not

money - 10; 

the first decrement allowed second expression (represents value).