import java.io.*; import java.math.BigDecimal; import java.util.*; @SuppressWarnings("unused") public class Main { FastScanner in; PrintWriter out; final static int MOD = (int)1e9+7; void solve(){ int N = in.nextInt(); long[] A = in.nextLongArray(N); MultiSet L = new MultiSet<>(), R = new MultiSet<>(); for(int i = 0; i < N; i++) R.add(A[i]); long min = Long.MAX_VALUE; for(int i = 0; i < N; i++){ R.sub(A[i]); if(!L.isEmpty() && !R.isEmpty()){ Long vl = L.firstKey(), vr = R.firstKey(); if(vl != null && vr != null && vl < A[i] && vr < A[i]) min = Math.min(min, vl + A[i] + vr); } { Long vl = L.higherKey(A[i]), vr = R.higherKey(A[i]); if(vl != null && vr != null) min = Math.min(min, vl + A[i] + vr); } L.add(A[i]); } out.println(min == Long.MAX_VALUE ? "-1" : min); } class MultiSet> extends TreeMap{ int sum = 0; public int sum(){ return this.sum; } public int count(K k){ return this.getOrDefault(k, 0); } public int add(K k) { int res = this.count(k) + 1; this.put(k, res); sum++; return res; } public int sub(K k){ if(!this.containsKey(k)) return -1; int res = this.count(k) - 1; if(res == 0) this.remove(k); else this.put(k, res); sum--; return res; } public int subAll(K k){ if(!this.containsKey(k)) return -1; int cnt = this.count(k); this.remove(k); sum -= cnt; return cnt; } } public static void main(String[] args) { new Main().m(); } private void m() { in = new FastScanner(System.in); out = new PrintWriter(System.out); /* try { String path = "input.txt"; out = new PrintWriter(new BufferedWriter(new FileWriter(new File(path)))); }catch (IOException e){ e.printStackTrace(); } */ solve(); out.flush(); in.close(); out.close(); } static class FastScanner { private Reader input; public FastScanner() {this(System.in);} public FastScanner(InputStream stream) {this.input = new BufferedReader(new InputStreamReader(stream));} public void close() { try { this.input.close(); } catch (IOException e) { e.printStackTrace(); } } public int nextInt() { long nl = nextLong(); if (nl < Integer.MIN_VALUE || nl > Integer.MAX_VALUE) throw new NumberFormatException(); return (int) nl; } public long nextLong() { try { int sign = 1; int b = input.read(); while ((b < '0' || '9' < b) && b != '-' && b != '+') { b = input.read(); } if (b == '-') { sign = -1; b = input.read(); } else if (b == '+') { b = input.read(); } long ret = b - '0'; while (true) { b = input.read(); if (b < '0' || '9' < b) return ret * sign; ret *= 10; ret += b - '0'; } } catch (IOException e) { e.printStackTrace(); return -1; } } public double nextDouble() { try { double sign = 1; int b = input.read(); while ((b < '0' || '9' < b) && b != '-' && b != '+') { b = input.read(); } if (b == '-') { sign = -1; b = input.read(); } else if (b == '+') { b = input.read(); } double ret = b - '0'; while (true) { b = input.read(); if (b < '0' || '9' < b) break; ret *= 10; ret += b - '0'; } if (b != '.') return sign * ret; double div = 1; b = input.read(); while ('0' <= b && b <= '9') { ret *= 10; ret += b - '0'; div *= 10; b = input.read(); } return sign * ret / div; } catch (IOException e) { e.printStackTrace(); return Double.NaN; } } public char nextChar() { try { int b = input.read(); while (Character.isWhitespace(b)) { b = input.read(); } return (char) b; } catch (IOException e) { e.printStackTrace(); return 0; } } public String nextStr() { try { StringBuilder sb = new StringBuilder(); int b = input.read(); while (Character.isWhitespace(b)) { b = input.read(); } while (b != -1 && !Character.isWhitespace(b)) { sb.append((char) b); b = input.read(); } return sb.toString(); } catch (IOException e) { e.printStackTrace(); return ""; } } public String nextLine() { try { StringBuilder sb = new StringBuilder(); int b = input.read(); while (b != -1 && b != '\n') { sb.append((char) b); b = input.read(); } return sb.toString(); } catch (IOException e) { e.printStackTrace(); return ""; } } public int[] nextIntArray(int n) { int[] res = new int[n]; for (int i = 0; i < n; i++) { res[i] = nextInt(); } return res; } public int[] nextIntArrayDec(int n) { int[] res = new int[n]; for (int i = 0; i < n; i++) { res[i] = nextInt() - 1; } return res; } public int[] nextIntArray1Index(int n) { int[] res = new int[n + 1]; for (int i = 0; i < n; i++) { res[i + 1] = nextInt(); } return res; } public long[] nextLongArray(int n) { long[] res = new long[n]; for (int i = 0; i < n; i++) { res[i] = nextLong(); } return res; } public long[] nextLongArrayDec(int n) { long[] res = new long[n]; for (int i = 0; i < n; i++) { res[i] = nextLong() - 1; } return res; } public long[] nextLongArray1Index(int n) { long[] res = new long[n + 1]; for (int i = 0; i < n; i++) { res[i + 1] = nextLong(); } return res; } public double[] nextDoubleArray(int n) { double[] res = new double[n]; for (int i = 0; i < n; i++) { res[i] = nextDouble(); } return res; } } }