#include<stdio.h>

int main(){
    int N, i, j,found = 0;
    scanf("%d",&n);
    if (N< 0){
        printf("Invalid input");
        return 0;
    }
    for (i=0; i<n; i++){ 
        scanf("%d",&arr[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;
}
}