#include <stdio.h>
int main (){
    int N;
    scanf("%d",&N);
    int arr [N];
    for (int i=0;i<N;i++){
    scanf("%d",&arr[i]);
}
int duplicate[N];
int dupCount=0;
for(int i=0;i<N;i++){
for (int j=i+1;j<N;j++){
    if (arr[i]==arr[j]){
        int alreadyAdded = 0;
        for(int k=0;k<dupCount;k++){
            if(duplicate[k]==arr[i]){
                alreadyAdded=1;
                break;
            }
        }
        if(!alreadyAdded){
            duplicate[dupCount++]=arr[i];
    
            }
        }
    }
}
if(dupCount ==0){
    printf("No duplicate\n");
}
else{
    for (int i=0;i<dupCount;i++)
    printf("%d",duplicate[i]);
}
printf("\n");
}
return 0;
}