Android : Unfortunately, myApplicaiton has stopped in Android studio

I have an application which uses google map api. I tried so hard to figure out what my application crashes right the moment it starts to run and displays a pop-up saying "Unfortunately, myApplicaiton has stopped ". I spent many hours to see where else I should look into the code. Any tips will be appreciated.

Here is the code (MainActivity.java:89-95)

protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        requestWindowFeature(Window.FEATURE_NO_TITLE);
        getWindow().addFlags(WindowManager.LayoutParams.FLAG_KEEP_SCREEN_ON);
        setContentView(R.layout.activity_main);         //(MainActivity.java:93)
        StrictMode.ThreadPolicy policy = new StrictMode.ThreadPolicy.Builder()
                .permitAll().build();

and here is the error log

12-13 15:26:35.724    7875-7875/com.example.myApplication E/AndroidRuntime﹕ FATAL EXCEPTION: main
    java.lang.NoClassDefFoundError: com.google.android.gms.R$styleable
            at com.google.android.gms.maps.GoogleMapOptions.createFromAttributes(Unknown Source)
            at com.google.android.gms.maps.SupportMapFragment.onInflate(Unknown Source)
            at android.support.v4.app.FragmentManagerImpl.onCreateView(FragmentManager.java:2158)
            at android.support.v4.app.FragmentActivity.onCreateView(FragmentActivity.java:297)
            at android.view.LayoutInflater.createViewFromTag(LayoutInflater.java:676)
            at android.view.LayoutInflater.rInflate(LayoutInflater.java:746)
            at android.view.LayoutInflater.inflate(LayoutInflater.java:489)
            at android.view.LayoutInflater.inflate(LayoutInflater.java:396)
            at android.view.LayoutInflater.inflate(LayoutInflater.java:352)
            at com.android.internal.policy.impl.PhoneWindow.setContentView(PhoneWindow.java:270)
            at android.app.Activity.setContentView(Activity.java:1881)
            at com.example.selflocation.MainActivity.onCreate(MainActivity.java:93)
            at android.app.Activity.performCreate(Activity.java:5104)
            at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1080)
            at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2144)
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2230)
            at android.app.ActivityThread.access$600(ActivityThread.java:141)
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1234)
            at android.os.Handler.dispatchMessage(Handler.java:99)
            at android.os.Looper.loop(Looper.java:137)
            at android.app.ActivityThread.main(ActivityThread.java:5039)
            at java.lang.reflect.Method.invokeNative(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:511)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560)
            at dalvik.system.NativeStart.main(Native Method)