input()
arr = list(int(n) for n in input().split(" "))
biggest = max(arr)

def fix():
    index = 0
    while index+1 < len(arr):
        if arr[index] == arr[index+1]:
            arr[index]*=2
            arr.pop(index+1)
            index-=2
        index+=1

fix()
num = 1
while num < biggest:
    fix()
    other = -1
    i = 0
    while i < len(arr):
        if arr[i] == num:
            if other == -1:
                other = i
            else:
                index = other
                sum = 0
                while index < i and sum < 2*num:
                    sum+=arr[index]
                    index+=1
                if sum >= 2*num:
                    arr.pop(i)
                    arr.pop(other)
                    i-=2
                other = -1
        i+=1
    if other != -1:
        arr.pop(other)
    num*=2

print(arr[0])