n = int(input())
a = list(map(int,input().split()))
aup = sorted(a)
adown = sorted(a, reverse=True)
if a == aup or a == adown:
    print(-1)
    exit()
minl = [a[0]]
minr = [a[-1]]
nmin = a[0]
for i in range(1,n):
    minl.append(nmin)
    if nmin > a[i]:
        nmin = a[i]
nmin = a[-1]
for i in range(n-2, -1, -1):
    minr.append(nmin)
    if nmin > a[i]:
        nmin = a[i]
minr.reverse()
ans = int(1e12)
for i in range(1, n-1):
    if minl[i] < a[i] and minr[i] < a[i]:
        ans = min(ans, a[i]+minl[i]+minr[i])
    if a[i] < minl[i] and a[i] < minr[i]:
        ans = min(ans, a[i]+minl[i]+minr[i])
print(ans)