Static Synchronized Method Behavior

Consider the following code. What is the effect of declaring the increment method as static synchronized?

public class StaticInstanceSync {
    private static int counter = 0;
    
    public static synchronized void increment() {
        counter++;
    }
    
    public void runTask() {
        for(int i = 0; i < 1000; i++) {
            increment();
        }
    }
    
    public static void main(String[] args) throws InterruptedException {
        StaticInstanceSync sis1 = new StaticInstanceSync();
        StaticInstanceSync sis2 = new StaticInstanceSync();
        Thread t1 = new Thread(() -> sis1.runTask());
        Thread t2 = new Thread(() -> sis2.runTask());
        t1.start();
        t2.start();
        t1.join();
        t2.join();
        System.out.println(counter);
    }
}