#include <bits/stdc++.h>
using namespace std;
 
#define hell 1000000007
#define PI acos(-1.0)
#define S second
#define F first
#define pb push_back
#define endl '\n'
#define lli long long int
#define li long int
#define ld long double
#define all(v) v.begin(), v.end()
 
#define run(j, n) for(auto ii=j;ii!=n;ii++)
#define out(j, n) for(auto ii=j;ii!=n;ii++) cout<<(*ii)<<" ";
#define sout(ar, i, n) for(int j=i;j<n;j++) cout<<ar[j]<<" ";
 

int main() {
ios_base::sync_with_stdio(0);
cin.tie(0);
cout << fixed << showpoint;
cout << setprecision(11);
 
int n;cin>>n;
lli ar[n];run(0, n) cin>>ar[ii];

lli v1[2][n], v2[2][n];
v1[0][0]=ar[0];
v1[1][0]=ar[0];  

v2[0][n-1]=ar[n-1];
v2[1][n-1]=ar[n-1];
for(int i=1;i<n;i++)
{
  v1[0][i]=min(v1[0][i-1], ar[i]);
  v1[1][i]=max(v1[1][i-1], ar[i]);

}


for(int i=n-2;i>=0;i--)
{
  v2[0][i]=min(v2[0][i+1], ar[i]);
  v2[1][i]=max(v2[1][i+1], ar[i]);
}



lli ans = LLONG_MAX;

for(int i=0;i<n;i++)
{
  if(ar[i]!=v1[0][i] && ar[i]!=v2[0][i])
  {
    ans = min(ans, ar[i]+v1[0][i]+v2[0][i]);
  }
  if(ar[i]!=v1[1][i] && ar[i]!=v2[1][i])
  {
    ans = min(ans, ar[i]+v1[1][i]+v2[1][i]);
  }
}
if(ans==LLONG_MAX) ans = -1;
cout<<ans;
return 0;
}