Problem:
Score : 100 points

Problem Statement

You are given a positive integer N.
Find the minimum positive integer divisible by both 2 and N.

Constraints

1 \leq N \leq 10^9

All values in input are integers.

Input

Input is given from Standard Input in the following format:

N

Output

Print the minimum positive integer divisible by both 2 and N.

Sample Input 1

3

Sample Output 1

6

6 is divisible by both 2 and 3.
Also, there is no positive integer less than 6 that is divisible by both 2 and 3.
Thus, the answer is 6.

Sample Input 2

10

Sample Output 2

10

Sample Input 3

999999999

Sample Output 3

1999999998

Solution in C++14 (GCC 5.4.1) (judge verdict: Accepted)

#include <bits/stdc++.h> 
#define FOR(i,a,b) for(int i=(a);i<=(b);++i) 
#define RFOR(i,a,b) for(int i=(a);i>=(b);--i) 
#define REP(i,n) for(int i=0;i<(n);++i)
#define RREP(i,n) for(int i=(n);i>0;--i)
#define CI cin>> 
#define CO cout<<
#define EN <<endl 
#define all(x) (x).begin(),(x).end() 
using namespace std;
template <typename T> istream& operator >> (istream& is, vector<T>& vec) { for (T& x : vec) is >> x; 	return is; }
using ll = long long;

double inputData();
double calcArea();
double outputData();

int main(){
	int a; CI a;
	if (a % 2){ CO a * 2 EN; }
	else CO a EN;

	return 0;
}