#include <bits/stdc++.h>
using namespace std;
using LL = long long int;
#define incID(i, l, r) for(int i = (l)    ; i <  (r); ++i)
#define decID(i, l, r) for(int i = (r) - 1; i >= (l); --i)
#define incII(i, l, r) for(int i = (l)    ; i <= (r); ++i)
#define decII(i, l, r) for(int i = (r)    ; i >= (l); --i)
#define inc(i, n)  incID(i, 0, n)
#define dec(i, n)  decID(i, 0, n)
#define inc1(i, n) incII(i, 1, n)
#define dec1(i, n) decII(i, 1, n)
#define inID(v, l, r) ((l) <= (v) && (v) <  (r))
#define inII(v, l, r) ((l) <= (v) && (v) <= (r))
#define PB push_back
#define EB emplace_back
#define MP make_pair
#define MT make_tuple
#define FI first
#define SE second
#define FR front()
#define BA back()
#define ALL(v) v.begin(), v.end()
#define RALL(v) v.rbegin(), v.rend()
auto setmin   = [](auto & a, auto b) { return (b <  a ? a = b, true : false); };
auto setmax   = [](auto & a, auto b) { return (b >  a ? a = b, true : false); };
auto setmineq = [](auto & a, auto b) { return (b <= a ? a = b, true : false); };
auto setmaxeq = [](auto & a, auto b) { return (b >= a ? a = b, true : false); };
#define SI(v) static_cast<int>(v.size())
#define RF(e, v) for(auto & e: v)
#define until(e) while(! (e))
#define if_not(e) if(! (e))
#define ef else if
#define UR assert(false)
#define IN(T, ...) T __VA_ARGS__; IN_(__VA_ARGS__);
void IN_() { };
template<typename T, typename ... U> void IN_(T &  a, U &  ... b) { cin >> a; IN_(b ...); };
template<typename T                > void OUT(T && a            ) { cout << a << endl; }
template<typename T, typename ... U> void OUT(T && a, U && ... b) { cout << a << " "; OUT(b ...); }

// ---- ----

template<typename T> istream & operator>>(istream & s, vector<T> & v) { RF(e, v) { s >> e; } return s; }
template<typename T> ostream & operator<<(ostream & s, vector<T> const & v) {
	inc(i, SI(v)) { s << (i == 0 ? "" : " ") << v[i]; }
	return s;
}

int main() {
	IN(int, n);
	vector<int> a(n);
	cin >> a;
	
	const int INF = 1e9;
	
	set<int> se;
	vector<int> lmi(n, INF), lma(n, INF);
	inc(i, n) {
		auto mi = se.begin();
		auto ma = se.lower_bound(a[i]);
		if(mi != se.end() && *mi < a[i]) { lmi[i] = *mi; }
		if(ma != se.end()              ) { lma[i] = *ma; }
		se.insert(a[i]);
	}
	se.clear();
	vector<int> rmi(n, INF), rma(n, INF);
	dec(i, n) {
		auto mi = se.begin();
		auto ma = se.lower_bound(a[i]);
		if(mi != se.end() && *mi < a[i]) { rmi[i] = *mi; }
		if(ma != se.end()              ) { rma[i] = *ma; }
		se.insert(a[i]);
	}
	
	int ans = INF;
	incID(i, 1, n - 1) {
		setmin(ans, a[i] + lmi[i] + rmi[i]);
		setmin(ans, a[i] + lma[i] + rma[i]);
	}
	if(ans == INF) { ans = -1; }
	OUT(ans);
}