#include <iostream>
#include <string>
using namespace std;

int main() {
    string input;
    while (cin >> input) {
        if ((int) input.length() % 2 != 0) {
            cout << "NA" << endl;
            continue;
        }
        bool NAFlag = false;
        string output;
        while (input.length() > 0) {
            switch (input[0]) {
            case '1':
                output += 'a' + (input[1] - '0') - 1;
                break;
            case '2':
                output += 'f' + (input[1] - '0') - 1;
                break;
            case '3':
                output += 'k' + (input[1] - '0') - 1;
                break;
            case '4':
                output += 'p' + (input[1] - '0') - 1;
                break;
            case '5':
                output += 'u' + (input[1] - '0') - 1;
                break;
            case '6':
                switch (input[1]) {
                case '1':
                    output += 'z';
                    break;
                case '2':
                    output += '.';
                    break;
                case '3':
                    output += '?';
                    break;
                case '4':
                    output += '!';
                    break;
                case '5':
                    output += ' ';
                    break;
                default:
                    NAFlag = true;
                    break;
                }
                break;
            default:
                NAFlag = true;
                break;
            }
            if (NAFlag) {
                cout << "NA" << endl;
                continue;
            }
            input.erase(0, 2);
        }
        cout << output << endl;
    }
}