#include <iostream>
#include <vector>
using namespace std;
int main(){
    int n;cin>>n;
    vector<int> A(n),lmn(n+1),rmn(n+1),lmx(n+1),rmx(n+1);
    lmn[0] = rmn[0] = 1000000001;
    for(int i = 0; n > i; i++){
        cin>>A[i];
    }
    for(int i = 0; n > i; i++){
        lmn[i+1] = min(lmn[i],A[i]);
        lmx[i+1] = max(lmx[i],A[i]);
        rmn[i+1] = min(rmn[i],A[n-i-1]);
        rmx[i+1] = max(rmx[i],A[n-i-1]);

    }
    int ans = -1;
    for(int i = 1; n-1 > i; i++){
        if(lmn[i] < A[i] && rmn[n-i-1] < A[i]){
            if(ans == -1)ans = A[i]+lmn[i]+rmn[n-i-1];
            else ans = min(ans,A[i]+lmn[i]+rmn[n-i-1]);
        }
        if(lmx[i] > A[i] && rmx[n-i-1] > A[i]){
            if(ans == -1)ans = A[i]+lmx[i]+rmx[n-i-1];
            else ans = min(ans,A[i]+lmx[i]+rmx[n-i-1]);
        }
    }
    cout << ans << endl;
}