from math import log2

MAXV = 1005

n = int(input())
a = list(map(int, input().split()))
for i in range(n):
    a[i] = int(log2(a[i]))

dp = [[n for _ in range(MAXV)] for _ in range(n)]
res = 0
for i in range(n - 1, -1, -1):
    dp[i][a[i]] = i 
    for j in range(MAXV):
        if (i < n - 1):
            dp[i][j] = min(dp[i][j], dp[i + 1][j])
        if (dp[i][j - 1] + 1 < n):
            dp[i][j] = min(dp[i][j], dp[dp[i][j - 1] + 1][j - 1])
        if (dp[i][j] < n):
            res = max(res, j)

res = 2 ** res
print(res)