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

b = 30
def calc(k):
    x = [-1] * (b+1)
    for u in a:
        for j in range(b,-1,-1):
            mask = 1 << j
            if k & mask == 0 and u & mask:
                if x[j] == 0:return False
                elif x[j] == -1:
                    x[j] = 1
            elif k & mask == 0 and u & mask == 0:
                if x[j] == 1:return False
                elif x[j] == -1:
                    x[j] = 0
            elif k & mask:
                if x[j] == 1 and u & mask:
                    break
                if x[j] == 0 and u & mask == 0:
                    break
    return True
end = (1 << b+1) - 1
start = -1
while end - start > 1:
    mid = end + start >> 1
    if calc(mid):
        end = mid
    else:
        start = mid
print(end)