import java.util.Arrays;
import java.util.Scanner;

public class _1496 {
    public static void main(String[] args) {

        Scanner s = new Scanner(System.in);
        int amount = s.nextInt();
        if (amount == 0) System.out.println("0");
        else {
            String[] source = new String[amount];
            String[] uniT = new String[amount];
            int j = 0;
            int count = 0;
            for (int i = 0; i < amount; i++) {
                source[i] = s.nextLine();
            }
            Arrays.sort(source);
            uniT[0] = source[0];

            for (int i = 0; i < amount; i++) {
                if (source[i].equals(uniT[j]) != true) {
                    j++;
                    uniT[j] = source[i];
                }
            }
            for (int i = 0; i <= j; i++) {
                count = 0;
                for (int k = 0; k < amount; k++) {
                    if (source[k].equals(uniT[i])) {
                        count++;
                    }
                }
                if (count > 1) {
                    System.out.println(uniT[i]);
                }
            }
        }
    }
}

You have to change Output in case of empty solution from "0" to Empty string. It will solve your problem