#include<iostream>

 #include<cstdio>

 #include<cstring>

 #include<algorithm>

 #include<cmath>

 #define dbg(x) cerr << #x << " = " << x <<endl

 using namespace std;

 typedef long long ll;

 typedef double db;

 typedef pair<int,int> pii;

 template<typename T>inline T _min(T A,T B){return A<B?A:B;}

 template<typename T>inline T _max(T A,T B){return A>B?A:B;}

 template<typename T>inline char MIN(T&A,T B){return A>B?(A=B,):;}

 template<typename T>inline char MAX(T&A,T B){return A<B?(A=B,):;}

 template<typename T>inline void _swap(T&A,T&B){A^=B^=A^=B;}

 template<typename T>inline T read(T&x){

     x=;int f=;char c;while(!isdigit(c=getchar()))if(c=='-')f=;

     while(isdigit(c))x=x*+(c&),c=getchar();return f?x=-x:x;

 }

 const int N=+;

 int A[N];

 int n;

 int main(){//freopen("test.in","r",stdin);//freopen("test.out","w",stdout);

     while(read(n)){

         for(register int i=;i<=n;++i)read(A[i]);

         if(n&)puts("");

         else{

             sort(A+,A+n+);register int i;

             for(i=;i<=n;i+=)if(A[i]^A[i+]){puts("");break;}

             if(i>n)puts("");

         }

     }

     return ;

 }