The word Hosanna has many meanings: "help", "save, I pray", "Save, now!" or Praising etc.
If the people shouted "Hosanna" in order to praise Jesus merely as a great Prophet, it would be easier to shout "Crucify him!" later when they were disappointed by his acts.
If the intention of the people of Jerusalem was to say "Save us from the hands of Rome", it means they accepted Jesus as the Messiah after seeing all the miracles he performed. But in less than a week they became impatient and shouted "Crucify him!", thereby rushing to a conclusion that Jesus was actually not the Messiah.
What was the intention of the people of Jerusalem when they shouted Hosanna?