#include <bits/stdc++.h>
using namespace std;

const string characters = "abcdefghijklmnopqrstuvwxyz.?! ";

string convert(const string &number) {
	if(number.size() & 1) return "NA";

	string res = "";
	for(unsigned i = 0; i < number.size(); i += 2) {
		if(!('1' <= number[i] && number[i] <= '6')) return "NA";
		if(!('1' <= number[i + 1] && number[i + 1] <= '5')) return "NA";


		const unsigned idx = (number[i] - '1') * 5 + (number[i + 1] - '1');

		if(idx >= characters.size()) return "NA";

		res += characters[idx];
	}

	return res;
}

int main() {
	string number;
	while(cin >> number) {
		cout << convert(number) << endl;
	}

	return EXIT_SUCCESS;
}