How many years difference is there between the first year of the two Crimean campaigns and the last time Crimea was approached by Russian forces?
return the  first year of the   two Crimean campaigns ;return year of #1 ;return the  last time Crimea was  approached by Russian forces ;return year of #3 ;return difference of #2 and  #4
['select', 'project', 'select', 'project', 'arithmetic']