How many years after the start of the First Goryeo-Khitan War did King Seongjong die?
return the  start of the First Goryeo-Khitan War ;return King Seongjong dies ;return year of #1 ;return year of #2 ;return the  difference of #4 and  #3
['select', 'select', 'project', 'project', 'arithmetic']