open System

let rec insertions x = function
    | []             -> [[x]]
    | (y :: ys) as l -> (x::l)::(List.map (fun x -> y::x) (insertions x ys))

let rec permutations = function
    | []      -> seq [ [] ]
    | x :: xs -> Seq.concat (Seq.map (insertions x) (permutations xs))

let ri () = stdin.ReadLine() |> int
let ria () = stdin.ReadLine().Split() |> Array.map int

let zip3 a b c =
    Seq.zip a b 
    |> Seq.zip c
    |> Seq.map (fun (z,(x,y)) -> (x,y,z) )

let isKadmatsu (x,y,z) = ( x <> y ) && ( y <> z) && (x <> z) && ( ((x < y) && (y > z)) || ((x > y) && (y < z)))
let isAscendingKadomatsu ((x:int),(y:int),(z:int)) = ( isKadmatsu (x,y,z) ) && (x < z)

let isAscendingKadomatsuSeq (a:int list) = 
    let a3 = zip3 a (Seq.skip 1 a) (Seq.skip 2 a)
    a3 |> Seq.map isAscendingKadomatsu |> Seq.reduce (fun x s -> x && s)
    
type Sol() =
    member this.Solve() = 
        let D = ria() |> Array.toList
        let permu = permutations D
        
        let ret = Seq.tryFind  (fun ar -> isAscendingKadomatsuSeq ar ) permu
        if (Option.isSome ret) then "YES" else "NO"
        |> printfn "%s"
                                   
        
        
let mySol = new Sol()
mySol.Solve()