import java.util.*;
public class Main {
public static void main(String[] args){
Scanner sc = new Scanner(System.in);
int count = sc.nextInt();
int[] arr = new int[count];
int res = 0;
for(int i=0;i<count;i++){
arr[i] = sc.nextInt();
res ^= arr[i];
}
System.out.println(res);
}
} import java.util.Scanner;
import java.util.Arrays;
public class Main{
public static void main(String[] args){
Scanner sc=new Scanner(System.in);
int n=sc.nextInt();
int[] arr=new int[n];
for(int i=0;i<n;i++){
arr[i]=sc.nextInt();
}
Arrays.sort(arr);
for(int i=0;i<n-1;){
if(arr[i]!=arr[i+1]){
System.out.print(arr[i]);
break;
}
i=i+2;
}
}
} public static void test(int[] data) {
//题解: 例如 5^5=0。
int flag = 0;
for (int ele : data) {
flag = flag ^ ele;
}
System.out.println(flag);
}