#include<stdio.h>

int main(){
    int n;
    scanf("%d",&n);
    int ids[n];
    int i,j;
    int found=0;
    
    for(i=0;i<n;i++){
        scanf("%d",&ids[i]);
    }
    
    for(i=0;i<n;i++){
        for(j=i=1;j<n;j++){
            if(ids[i]==ids[j]){
                printf("%d",ids[i]);
                found=1;
                break;
            }
        }
    }
    if(!found){
        printf("No duplicate found");
    }
    return 0;
}