#include<bits/stdc++.h>
using namespace std;
void fastscan(int &x)
{
bool neg=false;
register int c;
x =0;
c=getchar();
if(c=='-')
{
neg = true;
c=getchar();
}
for(;(c>47 && c<58);c=getchar())
x = (x<<1) + (x<<3) +c -48;
if(neg)
x *=-1;
}
int main()
{
int a,b,c,d,e,f,g,h;
vector <int> ve;
fastscan(a);
h=0;
for(b=0;b<a;b++)
{fastscan(g);
ve.push_back(g);
}
sort(ve.begin(),ve.end());
for(b=0;b<a;b++)
{
if(b==0)
{
if(ve[b]!=ve[b+1])
{
break;
}
}
else if(b==a-1)
{
if(ve[b]!=ve[b-1])
{
break;
}
}
else
{
if(ve[b]!=ve[b-1] && ve[b]!=ve[b+1])
break;
}
}
cout<<ve[b]<<"\n";}
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