import std.conv, std.functional, std.range, std.stdio, std.string;
import std.algorithm, std.array, std.bigint, std.bitmanip, std.complex, std.container, std.math, std.mathspecial, std.numeric, std.regex, std.typecons;
import core.bitop;

class EOFException : Throwable { this() { super("EOF"); } }
string[] tokens;
string readToken() { for (; tokens.empty; ) { if (stdin.eof) { throw new EOFException; } tokens = readln.split; } auto token = tokens.front; tokens.popFront; return token; }
int readInt() { return readToken.to!int; }
long readLong() { return readToken.to!long; }
real readReal() { return readToken.to!real; }

bool chmin(T)(ref T t, in T f) { if (t > f) { t = f; return true; } else { return false; } }
bool chmax(T)(ref T t, in T f) { if (t < f) { t = f; return true; } else { return false; } }

int binarySearch(alias pred, T)(in T[] as) { int lo = -1, hi = cast(int)(as.length); for (; lo + 1 < hi; ) { const mid = (lo + hi) >> 1; (unaryFun!pred(as[mid]) ? hi : lo) = mid; } return hi; }
int lowerBound(T)(in T[] as, T val) { return as.binarySearch!(a => (a >= val)); }
int upperBound(T)(in T[] as, T val) { return as.binarySearch!(a => (a > val)); }


enum INF = 10L^^18;

void main() {
  try {
    for (; ; ) {
      const N = readInt();
      auto A = new long[N];
      foreach (i; 0 .. N) {
        A[i] = readLong();
      }
      
      auto ls0 = new long[N];
      auto ls1 = new long[N];
      auto rs0 = new long[N];
      auto rs1 = new long[N];
      
      auto set = new RedBlackTree!long;
      set.clear;
      foreach (i; 0 .. N) {
        if (0 < i) {
          ls0[i] = (set.front < A[i]) ? set.front : INF;
          auto ran = set.upperBound(A[i]);
          ls1[i] = ran.empty ? INF : ran.front;
        }
        set.insert(A[i]);
      }
      set.clear;
      foreach_reverse (i; 0 .. N) {
        if (i < N - 1) {
          rs0[i] = (set.front < A[i]) ? set.front : INF;
          auto ran = set.upperBound(A[i]);
          rs1[i] = ran.empty ? INF : ran.front;
        }
        set.insert(A[i]);
      }
      debug {
        writeln("ls0 = ", ls0);
        writeln("ls1 = ", ls1);
        writeln("rs0 = ", rs0);
        writeln("rs1 = ", rs1);
      }
      
      long ans = INF;
      foreach (i; 1 .. N - 1) {
        chmin(ans, ls0[i] + A[i] + rs0[i]);
        chmin(ans, ls1[i] + A[i] + rs1[i]);
      }
      writeln((ans >= INF) ? -1 : ans);
    }
  } catch (EOFException e) {
  }
}