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

public class Zada4i3 {
    public static void main(String args[]) {

        Scanner scanner = new Scanner(System.in);

        String[] words = scanner.nextLine().split(" ");
        int count = 0;
        String[] wordsDis = new String[count];


        for (int i = 0; i < words.length - 1; i++) {

            if (!words[i].equals(words[i + 1])) {
                for (int j = i+1; j < words.length; j++) {

                    if (!words[i].equals(words[j])) {
                        count++;
                    }

                    if (count == (words.length - 1) - i) {
                        System.out.println(words[i]);
                        count = 0;
                    }

                }

            }
        }

        //last element
        int last = 0;
        for (int k = 0; k < words.length - 1; k++) {
            if (!words[words.length - 1].equals(words[k])) {
                last++;
            }

            if (last == words.length-1){
                System.out.println(words[words.length - 1]);

            }

        }

    }
}