package main

import (
	"fmt"
	"bufio"
	"os"
	"sort"
	"math"
)

func Min(a, b int) int {
	if a < b {
		return a
	} else {
		return b
	}
}

type SegmentTree struct {
	n int
	tree []int
}

func newSegmentTree(n int) *SegmentTree{
	sp := new(SegmentTree)
	sp.n = 1
	for sp.n < n {
		sp.n *= 2
	}
	sp.tree = make([]int, 2*sp.n)
	for i := 0; i < 2*sp.n; i++ {
		sp.tree[i] = math.MaxInt64
	}
	return sp
}

func (this *SegmentTree) set(idx, x int) {
	idx += this.n
	this.tree[idx] = x
	for idx > 0 {
		idx >>= 1
		this.tree[idx] = Min(this.tree[2 * idx], this.tree[2 * idx + 1])
	}
}

func (this *SegmentTree) query(lt, rt int) int {
	lt += this.n
	rt += this.n
	vl, vr := math.MaxInt64, math.MaxInt64
	for rt - lt > 0 {
		if lt & 1 != 0 {
			vl = Min(vl, this.tree[lt])
			lt++
		}
		if rt & 1 != 0 {
			rt--
			vr = Min(this.tree[rt], vr)
		}
		lt >>= 1
		rt >>= 1
	}
	return Min(vl, vr)
}

func main() {
	r := bufio.NewReader(os.Stdin)
	w := bufio.NewWriter(os.Stdout)
	defer w.Flush()
	var N int
	fmt.Fscan(r, &N)
	A := make([][2]int, N)
	for i := 0; i < N; i++ {
		var x int
		fmt.Fscan(r, &x)
		A[i] = [2]int{x, i}
	}
	sort.Slice(A, 
		func(i, j int) bool {
			if A[i][0] < A[j][0] {
				return true
			} else if A[i][0] > A[j][0] {
				return false
			} else {
				return A[i][1] < A[j][1]
			}
		})
	res := math.MaxInt64
	st1 := newSegmentTree(N)
	for i := 0; i < N; i++ {
		a, idx := A[i][0], A[i][1]
		st1.set(idx, a)
		lt := st1.query(0, idx)
		rt := st1.query(idx + 1, N)
		if lt == math.MaxInt64 || rt == math.MaxInt64 {
			continue
		}
		res = Min(res, lt + rt + a)
	}
	st2 := newSegmentTree(N)
	for i := N-1; i >= 0; i-- {
		a, idx := A[i][0], A[i][1]
		st2.set(idx, a)
		lt := st2.query(0, idx)
		rt := st2.query(idx + 1, N)
		if lt == math.MaxInt64 || rt == math.MaxInt64 {
			continue
		}
		res = Min(res, lt + rt + a)		
	}
	if res == math.MaxInt64 {
		fmt.Fprintln(w, -1)
	} else {
		fmt.Fprintln(w, res)
	}
}