import sys

sys.setrecursionlimit(200005)
int1 = lambda x: int(x)-1
p2D = lambda x: print(*x, sep="\n")
def II(): return int(sys.stdin.buffer.readline())
def LI(): return list(map(int, sys.stdin.buffer.readline().split()))
def LI1(): return list(map(int1, sys.stdin.buffer.readline().split()))
def LLI(rows_number): return [LI() for _ in range(rows_number)]
def LLI1(rows_number): return [LI1() for _ in range(rows_number)]
def BI(): return sys.stdin.buffer.readline().rstrip()
def SI(): return sys.stdin.buffer.readline().rstrip().decode()
dij = [(0, 1), (-1, 0), (0, -1), (1, 0)]
# dij = [(0, 1), (-1, 0), (0, -1), (1, 0), (1, 1), (1, -1), (-1, 1), (-1, -1)]
inf = 10**16
# md = 998244353
# md = 10**9+7

class BIT:
    def __init__(self, n):
        self.inf = 10**16
        self.n = n+3
        self.table = [self.inf]*(self.n+1)

    def update(self, i, x):
        i += 1
        while i <= self.n:
            if x < self.table[i]: self.table[i] = x
            i += i & -i

    def min(self, i):
        i += 1
        res = self.inf
        while i > 0:
            if self.table[i] < res: res = self.table[i]
            i -= i & -i
        return res

n = II()
aa = LI()
def make_mn(aa):
    res = []
    mn = inf
    for a in aa:
        if mn < a: res.append(mn)
        else: res.append(inf)
        mn = min(mn, a)
    return res

ll = make_mn(aa)
rr = make_mn(aa[::-1])[::-1]
ans = inf
for a, l, r in zip(aa, ll, rr):
    ans = min(ans, a+l+r)

def make_mx(aa):
    bit = BIT(n)
    res = [inf]*n
    for i, a in sorted(enumerate(aa), key=lambda x: -x[1]):
        mn = bit.min(i-1)
        res[i] = mn
        bit.update(i, a)
    return res

ll = make_mx(aa)
rr = make_mx(aa[::-1])[::-1]
for a, l, r in zip(aa, ll, rr):
    ans = min(ans, a+l+r)

if ans == inf: ans = -1
print(ans)