Codeforces 318A Even Odds

题目链接 ：http://codeforces.com/problemset/problem/318/A

A. Even Odds

time limit per test:1 second

memory limit per test:256 megabytes

input:standard input

output:standard output

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 %I64d specifier.

Output

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

Sample test(s)

Input
10 3

Output
5

Input
7 7

Output
6

Note

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.

一开始看到题目以为要用到大数相加，后来发现找找数学规律就好。

#include
typedef __int64 tt;
using namespace std;

int main()
{
    tt n,k;
    while(cin>>n>>k){
        if(n % 2 == 0)
        {
            if(k <= n/2)  cout <<2 *k -1;

                          else  cout << 2 *( k - n / 2);
        }
        else
        {
            if(k <= n / 2 + 1) cout << 2 *k -1;

               else cout<< 2 *( k - n / 2 - 1);
        } 

        cout<return 0;
}