class SegmentTree():
    def __init__(self, arr, func=min, ie=2**63):
        self.h = (len(arr) - 1).bit_length()
        self.n = 2**self.h
        self.ie = ie
        self.func = func
        self.tree = [ie for _ in range(2 * self.n)]
        for i in range(len(arr)):
            self.tree[self.n + i] = arr[i]
        for i in range(1, self.n)[::-1]:
            self.tree[i] = func(self.tree[2 * i], self.tree[2 * i + 1])

    def set(self, idx, x):
        idx += self.n
        self.tree[idx] = x
        while idx:
            idx >>= 1
            self.tree[idx] = self.func(self.tree[2 * idx], self.tree[2 * idx + 1])

    def query(self, lt, rt):
        lt += self.n
        rt += self.n
        vl = vr = self.ie
        while rt - lt > 0:
            if lt & 1:
                vl = self.func(vl, self.tree[lt])
                lt += 1
            if rt & 1:
                rt -= 1
                vr = self.func(self.tree[rt], vr)
            lt >>= 1
            rt >>= 1
        return self.func(vl, vr)

INF = 10**18

N = int(input())
A = list(map(int, input().split()))

S = sorted([(A[i], i) for i in range(N)])

res = INF

st1 = SegmentTree([INF] * N, min, INF)

for i in range(N):
    a, idx = S[i]
    st1.set(idx, a)
    lt = st1.query(0, idx)
    rt = st1.query(idx + 1, N)
    if lt == INF or rt == INF:
        continue
    res = min(res, lt + rt + a)

st2 = SegmentTree([INF] * N, min, INF)

for i in range(N)[::-1]:
    a, idx = S[i]
    st2.set(idx, a)
    lt = st2.query(0, idx)
    rt = st2.query(idx + 1, N)
    if lt == INF or rt == INF:
        continue
    res = min(res, lt + rt + a)

print(res if res != INF else -1)