#include<stdio.h>

#define Max_n 100
#define Max_id 2001
 void find_duplication(){
     int n;
     scanf("%d",&n);
     if(n < 1){
         printf("Invalid input");
         return 0;
     }
     int ids[max_n];
     int id_counts[max_id]={0};
     for(int i=0; i < n ;i++){
         scanf("%d",&ids[i]);
         id_counts[ids[i]+1000]++;
     }
     int found_duplication = 0;
     for(int i=0 ; i < max_n;i++){
         if(id_counts[ids[i]+1000] > 1){
             printf("%d",ids[i]);
             found_duplication 1;
             id_count[ids[i]+ 1000]=0;
         }
     }
     if(found_duplication){
         printf("No duplication found");
         return 0;
     }
 }
 int main(){
     find_duplicate(){
         return 0;
     }
 }