content: import java.io.*;
  import java.math.*;
  import java.security.*;
  import java.text.*;
  import java.util.*;
  import java.util.concurrent.*;
  import java.util.regex.*;
  
  public class Solution {
  
      // The method would return the unique value in the array
      // O(n) runtime. O(1) space. Uses XOR. Keep in mind:
      //   1) x ^ x = 0
      //   2) x ^ 0 = x
      //   3) XOR is commutative and associative
      static int lonelyinteger(int[] a) {
          // We would XOR all the numbers in the array
          // Only the unique number would be left
          int val = 0;
          for (int num : a) {
              val = val ^ num; // ^ is XOR operator
          }
          return val;
      }
      
      /* Driver Code */
      private static final Scanner scanner = new Scanner(System.in);
      public static void main(String[] args) throws IOException {
          BufferedWriter bufferedWriter = new BufferedWriter(new FileWriter(System.getenv("OUTPUT_PATH")));
          int n = scanner.nextInt();
          scanner.skip("(\r\n|[\n\r\u2028\u2029\u0085])?");
          int[] a = new int[n];
          String[] aItems = scanner.nextLine().split(" ");
          scanner.skip("(\r\n|[\n\r\u2028\u2029\u0085])?");
          for (int i = 0; i < n; i++) {
              int aItem = Integer.parseInt(aItems[i]);
              a[i] = aItem;
          }
          int result = lonelyinteger(a);
          bufferedWriter.write(String.valueOf(result));
          bufferedWriter.newLine();
          bufferedWriter.close();
          scanner.close();
      }
  }
  