How do I adding to score a collision? I'm beginner Thanks

How do I adding to score a collision? I'm beginner Thanks

Here is my code:

func didBeginContact(contact: SKPhysicsContact) {

    var firstBody: SKPhysicsBody
    var secondBody: SKPhysicsBody

       func addScore() {
        score = +1

    }

    if contact.bodyA.categoryBitMask < contact.bodyB.categoryBitMask {
        firstBody = contact.bodyA
        secondBody = contact.bodyB

    } else {
        firstBody = contact.bodyB
        secondBody = contact.bodyA

    }

    if ((firstBody.categoryBitMask & PhysicsCategory.monster != 0) &&
        (secondBody.categoryBitMask & PhysicsCategory.naboj != 0)) {

            if let firstNode = firstBody.node as? SKSpriteNode,
                let secondNode = secondBody.node as? SKSpriteNode  {

                    projectileDidCollideWithMonster(firstNode, monster: secondNode)
}

}

}

}