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

ans = float('inf')
first = A[0]
second = min(A[1:])
for i, a in enumerate(A[1:-1]):
    if second == a:
        second = min(A[2+i:])
    if (first - a) * (second - a) > 0:
        ans = min(ans, first + second + a)
    if first > a:
        first = a


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