eval'N,K,*A='+`dd`.split*?,
r=0
N.times{(N-K).times{|i|A[i],A[i+K]=A[i+K],A[i]if A[i]>A[i+K]&&r+=1}}
p (1...N).all?{|i|A[i-1]<A[i]}?r:-1