class ReverseEqual {
public:
bool checkReverseEqual(string s1, string s2) {
// write code here
if(s1.length()!=s2.length()) return false;
s1=s1+s1;
if(s1.find(s2)!=std:: npos) return true;
else return false;
}
};
#include<iostream>
#include<algorithm>
#include<cstring>
using namespace std;
const int maxn = 55;
int a[maxn];
int main()
{
int n,ans;
while(cin>>n)
{
int flag=0;
for(int i=0;i<n;++i)
{
cin>>a[i];
}
sort(a,a+n);
for(int i=1;i<n;++i)
{
if(a[i]-a[i-1]==1)
{
continue;
}
else if(a[i]-a[i-1]==2)
{
if(flag==2)
{
flag=1;
break;
}
ans=a[i]-1;
flag=2;
}
else
{
flag=1;
break;
}
}
if(flag==1)
{
cout<<"mistake"<<endl;
}else if(flag==2)
{
cout<<ans<<endl;
}else
{
if(a[0]==1)
{
cout<<a[n-1]+1<<endl;
}
else if(a[n-1]==1000000000)
{
cout<<a[0]-1<<endl;
}
else
{
cout<<a[0]-1<<" "<<a[n-1]+1<<endl;
}
}
}
return 0;
}