Codeforces Round #456 (Div. 2) B. New Year's Eve

最新推荐文章于 2022-12-16 16:19:21 发布

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原文链接：http://www.cnblogs.com/ACRykl/p/8215474.html

本文介绍了一个关于新年夜糖果选择的问题，目标是帮助Grisha从编号为1到n的糖果中选出不超过k个糖果，使得这些糖果编号的异或和最大。文章提供了问题的背景、输入输出要求及示例，并给出了C语言实现的代码。

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Since Grisha behaved well last year, at New Year's Eve he was visited by Ded Moroz who brought an enormous bag of gifts with him! The bag contains n sweet candies from the good ol' bakery, each labeled from 1 to n corresponding to its tastiness. No two candies have the same tastiness.

The choice of candies has a direct effect on Grisha's happiness. One can assume that he should take the tastiest ones — but no, the holiday magic turns things upside down. It is the xor-sum of tastinesses that matters, not the ordinary sum!

A xor-sum of a sequence of integers a₁, a₂, ..., a_m is defined as the bitwise XOR of all its elements: $\text{[math]}$ , here $\text{[math]}$ denotes the bitwise XOR operation; more about bitwise XOR can be found here.

Ded Moroz warned Grisha he has more houses to visit, so Grisha can take no more than k candies from the bag. Help Grisha determine the largest xor-sum (largest xor-sum means maximum happiness!) he can obtain.

Input

The sole string contains two integers n and k (1 ≤ k ≤ n ≤ 10¹⁸).

Output

Output one number — the largest possible xor-sum.

Examples

Input

4 3

Output

Input

6 6

Output

7

分析：k>1时，当数字n用二进制表示时，只要把所有数位变成1即可；
k=1直接输出n。

#include<cstdio>
int main()
{
    long long N,k;
    scanf("%lld%lld",&N,&k);
    if(k==1) printf("%lld\n",N);
    else
    {
        long long ans=1;
        while(true)
        {
            if(ans>N) break;
            ans=ans*2;
        }
        printf("%lld\n",ans-1);
    }
    return 0;
}