l = int(input());
ar = list(map(int,input().split()))
res = 0
for i in range(len(ar)):
    res = max(res,ar[i])
while len(ar) > 0:
    j = -1
    for i in range(1,len(ar)):
        if(ar[i] == ar[i-1]):
            j = i
            break
    mi = ar[j]
    for i in range(1,len(ar)):
        if(ar[i] == ar[i-1] and ar[i] < mi):
            mi = ar[i]
            j = i
    if j != -1:
        l = ar[j]
        ar.pop(j-1)
        ar.pop(j-1)
        ar.insert(j,2*l)
        res = max(res,2*l)
    else:
        m = ar[0]
        mi = 0
        for i in range(len(ar)):
            if(m > ar[i]):
                m = ar[i]
                mi = i
        ar.pop(mi);
print(res)