ActivityA --> ActivityB --> ActivityC --> ActivityD

ActivityF --> ActivityD
ActivityF finished

ActivityD

ActivityA --> ActivityB --> ActivityC --> ActivityD /// click back button
ActivityA --> ActivityB --> ActivityC /// click back button
ActivityA --> ActivityB /// click back button
ActivityA

ActivityA --> ActivityF --> ActivityD /// click back button
ActivityA --> ActivityF /// click back button
ActivityA

ActivityA
--> ActivityB
--> ActivityC
--> ActivityD /// click back button
ActivityC <-- /// click back button
ActivityB <-- /// click back button
ActivityA

ActivityA
--> ActivityF
--> ActivityD /// click back button
ActivityF <-- /// click back button
ActivityA <--

}