#include<iostream>
#include<string>
#include<algorithm>
#include<vector>
#include<iomanip>
#include<math.h>
#include<complex>
#include<queue>
#include<deque>
#include<stack>
#include<map>
#include<set>
#include<bitset>
#include<functional>
#include<assert.h>
#include<numeric>
using namespace std;
#define REP(i,m,n) for(int i=(int)(m) ; i < (int) (n) ; ++i )
#define rep(i,n) REP(i,0,n)
using ll = long long;
constexpr int inf=1e9+7;
constexpr ll longinf=1LL<<60 ;
constexpr ll mod=1e9+7 ;

int main(){
    cin.tie(nullptr);
    ios::sync_with_stdio(false);
    int n;
    cin>>n;
    vector<int> a(n+2);
    rep(i,n)cin>>a[i+1];
    vector<int> l(n+2,inf), r(n+2,inf);
    rep(i,n)l[i+1]=r[i+1]=a[i+1];
    rep(i,n+1)l[i+1]=min(l[i+1],l[i]);
    rep(i,n+1)r[n-i]=min(r[n-i],r[n-i+1]);
    int ans=inf;
    rep(i,n){
        if(l[i]<a[i+1]&&a[i+1]>r[i+2])ans=min(ans,l[i]+a[i+1]+r[i+2]);
        if(l[i]>a[i+1]&&a[i+1]<r[i+2])ans=min(ans,l[i]+a[i+1]+r[i+2]);
    }
    if(ans==inf)cout<<-1<<endl;
    else cout<<ans<<endl;
    return 0;
}