class SegmentTree:
    def __init__(self, size, f=min, default=10 ** 18):
        self.size = 2**(size-1).bit_length() 
        self.default = default
        self.dat = [default]*(self.size*2) 
        self.f = f

    def update(self, i, x):
        i += self.size
        self.dat[i] = x
        while i > 0:
            i >>= 1
            self.dat[i] = self.f(self.dat[i*2], self.dat[i*2+1])

    def query(self, l, r):
        l += self.size
        r += self.size
        lres, rres = self.default, self.default
        while l < r:
            if l & 1:
                lres = self.f(lres, self.dat[l])
                l += 1

            if r & 1:
                r -= 1
                rres = self.f(self.dat[r], rres) 
            l >>= 1
            r >>= 1
        res = self.f(lres, rres)
        return res


N = int(input())
A = list(map(int, input().split()))
B = [0] * N
for i in range(N):
    B[i] = (A[i], i + 1)
B.sort(reverse=True)

inf = 10 ** 18
T = SegmentTree(N + 2)
ans = inf
for a, i in B:
    x = T.query(0, i)
    y = T.query(i + 1, N + 2)
    ans = min(ans, x + a + y)
    T.update(i, a)
    
for i, a in enumerate(A):
    i += 1
    x = T.query(0, i)
    y = T.query(i + 1, N + 2)
    if x > a or y > a:
        continue
    ans = min(ans, x + a + y)

print(ans) if ans < inf else print(-1)