java.lang.IllegalStateException: Encountered inval

Question

I have the following method declaration:

@Scheduled(cron = "0 0 12 ? * MON#1")
protected synchronized void execute() {...}

But my application startup fails and I see following error in logs:

Caused by: java.lang.IllegalStateException: Encountered invalid @Scheduled method 'execute': For input string: "1#1"
    at org.springframework.scheduling.annotation.ScheduledAnnotationBeanPostProcessor.processScheduled(ScheduledAnnotationBeanPostProcessor.java:461) ~[spring-context-4.3.13.RELEASE.jar:4.3.13.RELEASE]
    at org.springframework.scheduling.annotation.ScheduledAnnotationBeanPostProcessor.postProcessAfterInitialization(ScheduledAnnotationBeanPostProcessor.java:331) ~[spring-context-4.3.13.RELEASE.jar:4.3.13.RELEASE]
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.applyBeanPostProcessorsAfterInitialization(AbstractAutowireCapableBeanFactory.java:423) ~[spring-beans-4.3.13.RELEASE.jar:4.3.13.RELEASE]
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.initializeBean(AbstractAutowireCapableBeanFactory.java:1633) ~[spring-beans-4.3.13.RELEASE.jar:4.3.13.RELEASE]
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:555) ~[spring-beans-4.3.13.RELEASE.jar:4.3.13.RELEASE]
    ... 19 common frames omitted

How to correct it?