#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
#define P pair<ll,ll>
#define FOR(I,A,B) for(ll I = ll(A); I < ll(B); ++I)
#define FORR(I,A,B) for(ll I = ll((B)-1); I >= ll(A); --I)
#define TO(x,t,f) ((x)?(t):(f))
#define SORT(x) (sort(x.begin(),x.end())) // 0 2 2 3 4 5 8 9
#define POSL(x,v) (lower_bound(x.begin(),x.end(),v)-x.begin()) //xi>=v  x is sorted
#define POSU(x,v) (upper_bound(x.begin(),x.end(),v)-x.begin()) //xi>v  x is sorted
#define NUM(x,v) (POSU(x,v)-POSL(x,v))  //x is sorted
#define REV(x) (reverse(x.begin(),x.end())) //reverse
ll gcd_(ll a,ll b){if(a%b==0)return b;return gcd_(b,a%b);}
ll lcm_(ll a,ll b){ll c=gcd_(a,b);return ((a/c)*(b/c)*c);}
#define NEXTP(x) next_permutation(x.begin(),x.end())
const ll INF=ll(1e16)+ll(7);
const ll MOD=1000000007LL;
//#define out(a) cout<<fixed<<setprecision((a))
//tie(a,b,c) = make_tuple(10,9,87);
#define pop_(a) __builtin_popcount((a))
ll keta(ll a){ll r=0;while(a){a/=10;r++;}return r;}



int main(){
	int N;
	cin >> N;
	set<int> f,b;
	int ans = MOD;
	vector<int> A(N);
	FOR(i,0,N)cin>>A[i],b.insert(A[i]);
	b.erase(A[0]);
	f.insert(A[0]);

	FOR(i,1,N-1){
		b.erase(A[i]);
		int a_min,a_max,c_min,c_max;
		a_min = *(f.begin());
		a_max = *(f.rbegin());
		c_min = *(b.begin());
		c_max = *(b.rbegin());
		if(A[i]>a_min && A[i]>c_min){
			ans = min(ans, A[i] + a_min  + c_min );
		}else if(A[i] < a_max && A[i] < c_max){
			auto x = f.lower_bound(A[i]);
			auto y = b.lower_bound(A[i]);
			ans = min(ans,A[i]+(*x)+(*y));
		}
		f.insert(A[i]);
	}
	if(ans==MOD)ans = -1;
	cout << ans << endl;
}