#include<bits/stdc++.h>
using namespace std;
int cx()
{	
    int Sign=1;
	char c;
	int x=0;
	while((c=getchar())>'9'||c<'0') 
		if(c=='-') Sign=-1;
	x=c-'0';	
	while((c=getchar())>='0'&&c<='9') 
		  x=(x<<3)+(x<<1)+c-'0';
	return x*Sign;
}
void print(int x)
{
  if(x<0) putchar('-');
  if(x/10) print(x/10);
  putchar(x%10+'0');
}
int main()
{
	int n,a,b=0;
	n=cx();
	for(int i=0;i<n;i++)
		{
		  a=Read();
		  b=b^a;
		}	
	print(b);
	return 0;
}