N = int(input())
lines = []
truelines = []
multy=1
i=-1
for q in range(0, N):
    lines.append(int(input()))
for line in lines:
    i+=1
    if line % 2 == 1:
        newlines = lines[i+6:]
        for newline in newlines:
            if newline % 2 == 1:
                multy=newline*line
                truelines.append(multy)
print(min(truelines) if truelines else -1)