:app:dexDebug UNEXPECTED TOP-LEVEL EXCEPTION:

I am building my project and after i add some codes from facebook for integration I faced :app:dexDebug UNEXPECTED TOP-LEVEL EXCEPTION: errors

Below is my build.gradle coding

apply plugin: 'com.android.application'

android { compileSdkVersion 20 buildToolsVersion "21.1.2"

repositories {
    mavenCentral()
}

defaultConfig {
    applicationId "com.hong.iqfunguess"
    minSdkVersion 9
    targetSdkVersion 21
}

buildTypes {
    release {
        minifyEnabled false
        proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.txt'
    }
} }

dependencies {

compile 'com.android.support:appcompat-v7:20.0.0'
compile 'com.android.support:support-v4:20.0.0'
compile 'com.facebook.android:facebook-android-sdk:4.0.0'
compile project(':facebook') }

The errors is show as listed below

Error:Execution failed for task ':app:dexDebug'.

com.android.ide.common.internal.LoggedErrorException: Failed to run command: E:\Android SDK\build-tools\21.1.2\dx.bat --dex --no-optimize --output C:\Users\Admin\Desktop\IQFunGuess April19\app\build\intermediates\dex\debug --input-list=C:\Users\Admin\Desktop\IQFunGuess April19\app\build\intermediates\tmp\dex\debug\inputList.txt Error Code: 2 Output: UNEXPECTED TOP-LEVEL EXCEPTION: com.android.dex.DexException: Multiple dex files define Lbolts/AggregateException; at com.android.dx.merge.DexMerger.readSortableTypes(DexMerger.java:596) at com.android.dx.merge.DexMerger.getSortedTypes(DexMerger.java:554) at com.android.dx.merge.DexMerger.mergeClassDefs(DexMerger.java:535) at com.android.dx.merge.DexMerger.mergeDexes(DexMerger.java:171) at com.android.dx.merge.DexMerger.merge(DexMerger.java:189) at com.android.dx.command.dexer.Main.mergeLibraryDexBuffers(Main.java:454) at com.android.dx.command.dexer.Main.runMonoDex(Main.java:303) at com.android.dx.command.dexer.Main.run(Main.java:246) at com.android.dx.command.dexer.Main.main(Main.java:215) at com.android.dx.command.Main.main(Main.java:106)

What's the problems? Thank you.