import Data.List
main=do
 [n,m]<-words<$>getLine
 ab<-map((\[a,b]->(a,b)).words).lines<$>getContents
 let s=[y|(x,y)<-ab,x=="1"]
 let t=[x|(x,y)<-ab,y==n]
 putStrLn$if length(intersect s t)>0 then"POSSIBLE"else"IMPOSSIBLE"