#include<iostream>
#include<string>
using namespace std;
int main() {
	string s;
	while (cin >> s){
		if (s.size() % 2 != 0) { 
			cout << "NA";
			goto P;
		}
		else 
			for (int i = 0; i < s.size(); i += 2){
			if (s[i] == '1'){
				if (s[i + 1] == '1')cout.put('a');
				else if (s[i + 1] == '2')cout.put('b');
				else if (s[i + 1] == '3')cout.put('c');
				else if (s[i + 1] == '4')cout.put('d');
				else if (s[i + 1] == '5')cout.put('e');
				else{
					cout << "NA";
					goto P;
				}
			}
			else if (s[i] == '2'){
				if (s[i + 1] == '1')cout.put('f');
				else if (s[i + 1] == '2')cout.put('g');
				else if (s[i + 1] == '3')cout.put('h');
				else if (s[i + 1] == '4')cout.put('i');
				else if (s[i + 1] == '5')cout.put('j');
				else {
					cout << "NA";
					goto P;
				}
			}
			else if (s[i] == '3'){
				if (s[i + 1] == '1')cout.put('k');
				else if (s[i + 1] == '2')cout.put('l');
				else if (s[i + 1] == '3')cout.put('m');
				else if (s[i + 1] == '4')cout.put('n');
				else if (s[i + 1] == '5')cout.put('o');
				else
				{
					cout << "NA";
					goto P;
				}
			}
			else if (s[i] == '4'){
				if (s[i + 1] == '1')cout.put('p');
				else if (s[i + 1] == '2')cout.put('q');
				else if (s[i + 1] == '3')cout.put('r');
				else if (s[i + 1] == '4')cout.put('s');
				else if (s[i + 1] == '5')cout.put('t');
				else {
					cout << "NA";
					goto P;
				}
			}
			else if (s[i] == '5') {
				if (s[i + 1] == '1')cout.put('u');
				else if (s[i + 1] == '2')cout.put('v');
				else if (s[i + 1] == '3')cout.put('w');
				else if (s[i + 1] == '4')cout.put('x');
				else if (s[i + 1] == '5')cout.put('y');
				else {
					cout << "NA";
					goto P;
				}
			}
			else if (s[i] == '6'){
				if (s[i + 1] == '1')cout.put('z');
				else if (s[i + 1] == '2')cout.put('.');
				else if (s[i + 1] == '3')cout.put('?');
				else if (s[i + 1] == '4')cout.put('!');
				else if (s[i + 1] == '5')cout.put(' ');
				else
				{
					cout << "NA";
					goto P;
				}
			}
			else {
				cout << "NA";
				goto P;
			}
		}
	P:
		cout << endl;
	}
}