Codeforces 276D. Little Girl and Maximum XOR

D. Little Girl and Maximum XOR

time limit per test

2 seconds

memory limit per test

256 megabytes

input

standard input

output

standard output

A little girl loves problems on bitwise operations very much. Here's one of them.

You are given two integers l and r. Let's consider the values of  for all pairs of integers a and b (l ≤ a ≤ b ≤ r). Your task is to find the maximum value among all considered ones.

Expression  means applying bitwise excluding or operation to integers x and y. The given operation exists in all modern programming languages, for example, in languages C++ and Java it is represented as "^", in Pascal — as «xor».

Input

The single line contains space-separated integers l and r (1 ≤ l ≤ r ≤ 1018).

Please, do not use the %lld specifier to read or write 64-bit integers in С++. It is preferred to use the cin, cout streams or the %I64dspecifier.

Output

In a single line print a single integer — the maximum value of  for all pairs of integers a, b (l ≤ a ≤ b ≤ r).

Sample test(s)

input

1 2

output

3

input

8 16

output

31

input

1 1

output

0

#include <stdio.h>

int main()
{
	unsigned long long l, r;
	unsigned long long finger = (unsigned long long)1 << 63;
	scanf("%I64u%I64u", &l, &r);
	if(l == r)
		finger = 0;
	else {
		while(!((l&finger) ^ (r&finger)))
			finger >>= 1;
		finger = (finger << 1) - 1;
	}
	printf("%I64u\n", finger);
	return 0;
}

我漏了第6行的强制类型转换，后来发现了这个错误。