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

MINL=[]
X=10**9
for a in A:
    X=min(a,X)
    MINL.append(X)

X=10**9
MINR=[]
for a in A[::-1]:
    X=min(a,X)
    MINR.append(X)

MINR=MINR[::-1]

ANS=3*10**9

for i in range(1,N-1):
    if A[i]>MINL[i-1] and A[i]>MINR[i+1]:
        ANS=min(ANS,A[i]+MINL[i-1]+MINR[i+1])

A1=A[0]
for i in range(1,N):
    if A[i]<A[i-1]:
        A1=A[i]
    else:
        break

#print(A1,i)
for j in range(i,N-1):
    if A[j]>A1 and MINR[j+1]<A[j]:
        ANS=min(ANS,A1+A[j]+MINR[j+1])

#print(ANS)


A1=A[-1]
for i in range(N-2,-1,-1):
    if A[i]<A[i+1]:
        A1=A[i]
    else:
        break

#print(A1,i)
 
for j in range(i,0,-1):
    if A[j]>A1 and MINL[j-1]<A[j]:
        ANS=min(ANS,A1+A[j]+MINL[j-1])


if ANS==3*10**9:
    print(-1)
else:
    print(ANS)