n=gets.to_i

aa=gets.split.map &:to_i

def isk(a,b,c)
  a!=c&&a<b&&b>c
end

m=0
z=nil
f=true
while(f)
  f=false
  n.times{|i|
    (i+1).upto(n){|j|
      (k+1).upto(n){|k|
        if isk(aa[i],aa[j],aa[k])
          z=[i,j,k] unless z
          f=true
          m+=1
          aa[i]=aa[j]=aa[k]=nil
        end
      }
    }
  }
  aa.delete(nil)
end

if m.even?
  puts -1
else
  puts z*' '
end