import java.util.Scanner;

public class DecodeMessage {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        String input = sc.nextLine().trim();
        sc.close();

        // check input length must be even
        if (input.length() % 2 != 0) {
            System.out.println("Invalid Input");
            return;
        }

        StringBuilder decoded = new StringBuilder();

        for (int i = 0; i < input.length(); i += 2) {
            String pair = input.substring(i, i + 2);
            int asciiVal = Integer.parseInt(pair);

            char ch = (char) asciiVal;

            // check if it's alphabet
            if ((ch >= 'A' && ch <= 'Z') || (ch >= 'a' && ch <= 'z')) {
                decoded.append(ch);
            } else {
                System.out.println("Invalid Input");
                return;
            }
        }

        System.out.println(decoded.toString());
    }
}