#include<iostream>
#include<vector>
#include<set>
signed main(){
    int n;
    std::cin>>n;
    std::vector<int> a(n);
    for(auto& ai:a)std::cin>>ai;
    int ans = (1LL<<28);
    std::set<int> lef,rig;
    lef.emplace(a[0]);
    for(int i=1;i<n;++i)rig.emplace(a[i]);
    for(int i=1;i+1<n;++i){
        rig.erase(a[i]);
        auto litr = lef.upper_bound(a[i]);
        auto ritr = rig.upper_bound(a[i]);
        if(litr!=std::end(lef)&&ritr!=std::end(rig)){
            ans = std::min(ans,*litr+a[i]+*ritr);
        }
        litr = std::begin(lef);
        ritr = std::begin(rig);
        if(*litr<a[i]&&*ritr<a[i]){
            ans = std::min(ans,*litr+a[i]+*ritr);
        }
        lef.emplace(a[i]);
    }
    std::cout << (ans==(1<<28)?-1:ans) << std::endl;
}