【打CF，学算法——一星级】CodeForces 318A （水题）

【CF简介】

提交链接：http://codeforces.com/problemset/problem/318/A

题面：

C - Even Odds
Time Limit:1000MS     Memory Limit:262144KB     64bit IO Format:%I64d
& %I64u
Submit Status

Description

Being a nonconformist, Volodya is displeased with the current state of things, particularly with the order of natural numbers (natural number is positive integer number). He is determined to rearrange them. But there are too many natural numbers, so Volodya
decided to start with the first n. He writes down the following sequence of numbers: firstly all odd integers from 1 to n (in
ascending order), then all even integers from 1 to n (also in ascending order). Help our hero to find out which number will stand at the
position number k.

Input

The only line of input contains integers n and k (1 ≤ k ≤ n ≤ 1012).

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

Output

Print the number that will stand at the position number k after Volodya's manipulations.

Sample Input

Input

10 3

Output

5

Input

7 7

Output

6

Hint

In the first sample Volodya's sequence will look like this: {1, 3, 5, 7, 9, 2, 4, 6, 8, 10}. The third place in the sequence is therefore occupied by the number 5.

题目大意：

    奇数在前，偶数在后，问第几个数是什么。好久没刷题了，签个到！

代码：

#include <iostream>
#include <algorithm>
#include <cstdio>
#include <cstring>
#include <cmath>
#include <vector>
#include <iomanip>
using namespace std;
#define inf 1e9
#define LL long long
#define ULL unsigned long long

int main()
{
long long a,b,mid;
scanf("%I64d%I64d",&a,&b);
mid=(a+1)/2;
if(b<=mid)
printf("%I64d\n",b*2-1);
else
printf("%I64d\n",(b-mid)*2);
return 0;
}