package main

import (
	"bufio"
	"fmt"
	"math"
	"os"
	"strconv"
	"strings"
)

var (
	y uint = 88172645463325252
)

func xorshift() uint {
	y ^= y << 7
	y ^= y >> 9
	return y
}

type treapNode struct {
	value    int
	priority uint
	count    int
	left     *treapNode
	right    *treapNode
}

func newTreapNode(v int) *treapNode {
	return &treapNode{v, xorshift(), 1, nil, nil}
}

func treapRotateRight(n *treapNode) *treapNode {
	l := n.left
	n.left = l.right
	l.right = n
	return l
}

func treapRotateLeft(n *treapNode) *treapNode {
	r := n.right
	n.right = r.left
	r.left = n
	return r
}

func treapInsert(n *treapNode, v int) *treapNode {
	if n == nil {
		return newTreapNode(v)
	}
	if n.value == v {
		n.count++
		return n
	}
	if n.value > v {
		n.left = treapInsert(n.left, v)
		if n.priority > n.left.priority {
			n = treapRotateRight(n)
		}
	} else {
		n.right = treapInsert(n.right, v)
		if n.priority > n.right.priority {
			n = treapRotateLeft(n)
		}
	}
	return n
}

func treapDelete(n *treapNode, v int) *treapNode {
	if n == nil {
		panic("node is not found!")
	}
	if n.value > v {
		n.left = treapDelete(n.left, v)
		return n
	}
	if n.value < v {
		n.right = treapDelete(n.right, v)
		return n
	}

	// n.value == v
	if n.count > 1 {
		n.count--
		return n
	}

	if n.left == nil && n.right == nil {
		return nil
	}

	if n.left == nil {
		n = treapRotateLeft(n)
	} else if n.right == nil {
		n = treapRotateRight(n)
	} else {
		// n.left != nil && n.right != nil
		if n.left.priority < n.right.priority {
			n = treapRotateRight(n)
		} else {
			n = treapRotateLeft(n)
		}
	}
	return treapDelete(n, v)
}

func treapCount(n *treapNode) int {
	if n == nil {
		return 0
	}
	return n.count + treapCount(n.left) + treapCount(n.right)
}

func treapString(n *treapNode) string {
	if n == nil {
		return ""
	}
	result := make([]string, 0)
	if n.left != nil {
		result = append(result, treapString(n.left))
	}
	result = append(result, fmt.Sprintf("%d:%d", n.value, n.count))
	if n.right != nil {
		result = append(result, treapString(n.right))
	}
	return strings.Join(result, " ")
}

func treapMin(n *treapNode) int {
	if n.left != nil {
		return treapMin(n.left)
	}
	return n.value
}

func treapGEMin(n *treapNode, v int) int {
	if n.value == v {
		return v
	}
	if n.value > v {
		if n.left != nil {
			return treapGEMin(n.left, v)
		}
		return n.value
	}
	// n.value < v
	if n.right != nil {
		return treapGEMin(n.right, v)
	}
	return math.MaxInt64
}

func treapMax(n *treapNode) int {
	if n.right != nil {
		return treapMax(n.right)
	}
	return n.value
}

type treap struct {
	root *treapNode
	size int
}

func (t *treap) Insert(v int) {
	t.root = treapInsert(t.root, v)
	t.size++
}

func (t *treap) Delete(v int) {
	t.root = treapDelete(t.root, v)
	t.size--
}

func (t *treap) String() string {
	return treapString(t.root)
}

func (t *treap) Count() int {
	return t.size
}

func (t *treap) Min() int {
	return treapMin(t.root)
}

func (t *treap) Max() int {
	return treapMax(t.root)
}

func (t *treap) GEMin(v int) int {
	return treapGEMin(t.root, v)
}

func min(x, y int) int {
	if x < y {
		return x
	}
	return y
}

func main() {
	defer flush()

	N := readInt()
	A := make([]int, N)
	for i := 0; i < N; i++ {
		A[i] = readInt()
	}

	lt := &treap{}
	rt := &treap{}
	lt.Insert(A[0])
	for i := 2; i < N; i++ {
		rt.Insert(A[i])
	}

	result := math.MaxInt64
	for i := 1; i < N-1; i++ {
		a := lt.Min()
		b := rt.Min()
		if a <= A[i] && b <= A[i] {
			//printf("凸 %d %d %d\n", a, A[i], b)
			result = min(result, a+A[i]+b)
		}

		c := lt.GEMin(A[i])
		d := rt.GEMin(A[i])
		if c != math.MaxInt64 && d != math.MaxInt64 && c >= A[i] && d >= A[i] {
			//printf("凹 %d %d %d\n", c, A[i], d)
			result = min(result, c+A[i]+c)
		}

		lt.Insert(A[i])
		rt.Delete(A[i+1])
	}
	if result == math.MaxInt64 {
		println(-1)
	} else {
		println(result)
	}
}

const (
	ioBufferSize = 1 * 1024 * 1024 // 1 MB
)

var stdinScanner = func() *bufio.Scanner {
	result := bufio.NewScanner(os.Stdin)
	result.Buffer(make([]byte, ioBufferSize), ioBufferSize)
	result.Split(bufio.ScanWords)
	return result
}()

func readString() string {
	stdinScanner.Scan()
	return stdinScanner.Text()
}

func readInt() int {
	result, err := strconv.Atoi(readString())
	if err != nil {
		panic(err)
	}
	return result
}

func readInts(n int) []int {
	result := make([]int, n)
	for i := 0; i < n; i++ {
		result[i] = readInt()
	}
	return result
}

var stdoutWriter = bufio.NewWriter(os.Stdout)

func flush() {
	stdoutWriter.Flush()
}

func printf(f string, args ...interface{}) (int, error) {
	return fmt.Fprintf(stdoutWriter, f, args...)
}

func println(args ...interface{}) (int, error) {
	return fmt.Fprintln(stdoutWriter, args...)
}