#include<stdio.h>

int main(){
    int n, i, j, k ids[100], dup=0;
    scanf("%d",&n);
    if (n< 1){
        printf("Invalid Input");
        return 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]){
        for (k=0; k<i;k++)
        if(ids[k] == ids[i])break;
        if (k ==i){
            printf("%d",ids[i]);
            dup = 1;
        }
    }
    if (!dup) printf("No duplicate found");
    return 0;
}