/* -*- coding: utf-8 -*-
 *
 * 1095.cc:  No.1095 Smallest Kadomatsu Subsequence - yukicoder
 */

#include<cstdio>
#include<cstdlib>
#include<cstring>
#include<cmath>
#include<iostream>
#include<string>
#include<vector>
#include<map>
#include<set>
#include<stack>
#include<list>
#include<queue>
#include<deque>
#include<algorithm>
#include<numeric>
#include<utility>
#include<complex>
#include<functional>
 
using namespace std;

/* constant */

const int MAX_N = 200000;
const int INF = 1 << 30;

/* typedef */

typedef set<int> si;

/* global variables */

int as[MAX_N];
si ls, rs;

/* subroutines */

/* main */

int main() {
  int n;
  scanf("%d", &n);

  for (int i = 0; i < n; i++) {
    scanf("%d", as + i);
    rs.insert(as[i]);
  }

  int minsum = INF;
  for (int i = 0; i < n; i++) {
    rs.erase(as[i]);
    if (! ls.empty() && ! rs.empty()) {
      int v0 = *(ls.begin()), v1 = *(rs.begin());
      if (v0 < as[i] && v1 < as[i]) {
	int sum = v0 + as[i] + v1;
	if (minsum > sum) minsum = sum;
      }
      else {
	si::iterator sit0 = ls.upper_bound(as[i]);
	si::iterator sit1 = rs.upper_bound(as[i]);
	if (sit0 != ls.end() && sit1 != rs.end()) {
	  int sum = *sit0 + as[i] + *sit1;
	  if (minsum > sum) minsum = sum;
	}
      }
    }
    ls.insert(as[i]);
  }

  printf("%d\n", (minsum < INF) ? minsum : -1);
  return 0;
}