Rajan and Odd frequency number

Given an array of numbers of size (2*n+1). Raja is unable to find the number which is present odd number of times.It is guaranteed that only one such number exists.Can you help Raja in finding the number which is present odd number of times?

Example:

Input:  n = 2, a = [1,2,3,2,1]
Output: 3

Approach

C++

#include <bits/stdc++.h>
using namespace std;

long long oddFrequency(long long n, long long a[])
{
    long long ans = a[0];
    for (long long i = 1; i < n; i++)
        ans = ans ^ a[i];
    return ans;
}
int main()
{
    long long n = 2;

    n = 2 * n + 1;
    long long a[n] = {1, 2, 3, 2, 1};

    cout << oddFrequency(n, a) << "\n";

    return 0;
}