package main

import (
	"bufio"
	"flag"
	"fmt"
	"io"
	"os"
	"strconv"
	"strings"
	"unicode"
)

// Function to decode number pairs into characters
func decodePair(pair string) rune {
	alphabet := " ABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789"
	num, err := strconv.Atoi(pair)
	if err != nil || num < 0 || num >= len(alphabet) {
		return rune(-1) // Return -1 if pair is not valid
	}
	return rune(alphabet[num])
}

// Function to apply the reverse shift and wrap around
func applyReverseShift(value, shift int) int {
	shifted := (value - shift) % 37
	if shifted < 0 {
		shifted += 37
	}
	return shifted
}

func main() {
	// Define command-line flags
	shift := flag.Int("s", 0, "Shift amount for the cipher")
	flag.Parse()

	// Read all input from stdin
	reader := bufio.NewReader(os.Stdin)
	inputBytes, _ := io.ReadAll(reader)
	input := string(inputBytes)

	// Remove all spaces and line breaks
	input = strings.ReplaceAll(input, " ", "")
	input = strings.ReplaceAll(input, "\n", "")
	input = strings.TrimSpace(input)

	var decoded strings.Builder

	// Decode the input string
	for i := 0; i < len(input); i += 2 {
		if i+1 >= len(input) {
			break // If there's an odd number of characters, break out
		}

		pair := input[i : i+2]
		num, err := strconv.Atoi(pair)
		if err != nil {
			continue // Skip invalid pairs
		}

		shiftedValue := applyReverseShift(num, *shift)
		char := decodePair(fmt.Sprintf("%02d", shiftedValue))
		if !unicode.IsPrint(char) || char == rune(-1) {
			continue // Skip invalid characters
		}

		decoded.WriteRune(char)
	}

	// Output the decoded string
	fmt.Println(decoded.String())
}