#include <iostream>
using namespace std;
int main() {
  int n;
  int a[200000+1];
  int i,j,k;

  cin >> n;
  for (i=0; i<n; i++) cin >> a[i];

  int min = 300000000+1;
  int x;
  for (i=0; i<n-2; i++) {
    for (j=i+1; j<n-1; j++) {
      for (k=j+1; k<n; k++) {
        if ((a[i] != a[k]) &&
            (((a[i] < a[j]) && (a[j] > a[k])) ||
             ((a[i] > a[j]) && (a[j] < a[k])))) {
          x = a[i]+a[j]+a[k];
          if (x < min) min = x;
        }
      }
    }
  }
  if (min == 300000000+1) min = -1;
  cout << min;
  return 0;
}