#input of int(split by space)
def get_i()
  return gets.chomp.split(" ").map(&:to_i)
end
#input of float(split by space)
def get_f()
  return gets.chomp.split(" ").map(&:to_f)
end
#input of string(split by space)
def get()
  return gets.chomp.split(" ")
end
#input of string(split per one character)
def get_nsp()
  return gets.chomp.split("")
end
#yes or no decision
def yn_judge(bool,y="Yes",n="No")
  return bool ? y : n 
end
#create of array
def array(size1,init=nil,size2=-1)
  if size2==-1
    return Array.new(size1){init}
  else
    return Array.new(size2){Array.new(size1){init}}
  end
end

def max(a,b)
    return a>b ? a : b
end

def min(a,b)
    return a>b ? b : a
end

INF=Float::INFINITY

N=gets.to_i
B=get_i
pls=Hash.new(0)
N.times do|i|
  if B[i]>i+1
      puts "-1"
      exit
  end  
end
(N-1).times do|i|
    if B[i]>B[i+1]
      pls[i]+=1
    end
end
ans=[]
seen=array(N,false)
seen[0]=true
ans.push(B[0])
(N-1).times do|i|
    (N-1).downto(1) do|j|
      if not seen[j] and i+2>=B[j]+pls[j]
          ans.push(B[j])
          seen[j]=true
          break
      end
    end
end
puts ans.join("\n")