import java.io.BufferedReader
import java.io.InputStream
import java.io.InputStreamReader
import java.util.*
import kotlin.math.abs
import kotlin.math.max
import kotlin.math.min

val MOD = 1_000_000_007L

class Solver(stream: InputStream, private val out: java.io.PrintWriter) {
  fun solve() {
    val N = ni()
    val A = nal(N)
    val set = TreeSet<Long>()
    val B = Array(N){Array(2){LongArray(2){-1} } }
    for (i in 0 until N) {
      val mn = if (set.isEmpty()) null else set.first()
      if (mn != null && mn < A[i]) B[i][0][0] = mn
      val gt = set.higher(A[i])
      if (gt != null && gt > A[i]) B[i][1][0] = gt
      set += A[i]
    }

    set.clear()
    for (i in N - 1 downTo 0) {
      val mn = if (set.isEmpty()) null else set.first()
      if (mn != null && mn < A[i]) B[i][0][1] = mn
      val gt = set.higher(A[i])
      if (gt != null && gt > A[i]) B[i][1][1] = gt
      set += A[i]
    }

    val INF = 1e18.toLong()
    var ans = INF
    for (i in 0 until N) {
      if (B[i][0][0] != -1L && B[i][0][1] != -1L) {
        ans = min(B[i][0].sum() + A[i], ans)
      }
    }

    if (ans == INF) out.println(-1)
    else out.println(ans)
  }













































  private val isDebug = try {
    // なんか本番でエラーでる
    System.getenv("MY_DEBUG") != null
  } catch (t: Throwable) {
    false
  }

  private var tokenizer: StringTokenizer? = null
  private val reader = BufferedReader(InputStreamReader(stream), 32768)
  private fun next(): String {
    while (tokenizer == null || !tokenizer!!.hasMoreTokens()) {
      tokenizer = StringTokenizer(reader.readLine())
    }
    return tokenizer!!.nextToken()
  }

  private fun ni() = next().toInt()
  private fun nl() = next().toLong()
  private fun ns() = next()
  private fun na(n: Int, offset: Int = 0): IntArray {
    return map(n) { ni() + offset }
  }
  private fun nal(n: Int, offset: Int = 0): LongArray {
    val res = LongArray(n)
    for (i in 0 until n) {
      res[i] = nl() + offset
    }
    return res
  }

  private fun na2(n: Int, offset: Int = 0): Array<IntArray> {
    val a  = Array(2){IntArray(n)}
    for (i in 0 until n) {
      for (e in a) {
        e[i] = ni() + offset
      }
    }
    return a
  }

  private inline fun map(n: Int, f: (Int) -> Int): IntArray {
    val res = IntArray(n)
    for (i in 0 until n) {
      res[i] = f(i)
    }
    return res
  }

  private inline fun debug(msg: () -> String) {
    if (isDebug) System.err.println(msg())
  }

  private fun debug(a: LongArray) {
    debug { a.joinToString(" ") }
  }

  private fun debug(a: IntArray) {
    debug { a.joinToString(" ") }
  }

  private fun debug(a: BooleanArray) {
    debug { a.map { if (it) 1 else 0 }.joinToString("") }
  }

  private fun debugDim(A: Array<LongArray>) {
    if (isDebug) {
      for (a in A) {
        debug(a)
      }
    }
  }
  private fun debugDim(A: Array<IntArray>) {
    if (isDebug) {
      for (a in A) {
        debug(a)
      }
    }
  }

  /**
   * 勝手にimport消されるのを防ぎたい
   */
  private fun hoge() {
    min(1, 2)
    max(1, 2)
    abs(-10)
  }
}

fun main() {
  val out = java.io.PrintWriter(System.out)
  Solver(System.`in`, out).solve()
  out.flush()
}