#include <iostream>
#include <string>
#include <cstdio>
#include <cmath>
#include <map>
#include <cstring>
#include <algorithm>
#define range(i,a,b) for(int i=a;i<=b;++i)
#define rerange(i,a,b) for(int i=a;i>=b;--i)
#define LL long long
#define fill(arr,tmp) memset(arr,tmp,sizeof(arr))
using namespace std;
map<int,int>MAP;
int n,tmp;
void init(){
cin>>n;
while(n--){
cin>>tmp;
MAP[tmp]++;
}
}
void solve(){
map<int,int>::iterator iter;
for(iter=MAP.begin();iter!=MAP.end();++iter)
if(iter->second==1){
cout<<iter->first<<endl;
return;
}
}
int main(){
init();
solve();
return 0;
}