#include <bits/stdc++.h>
using namespace std;
int main() {
  string s;
  while (cin >> s) {
    if (s.size() % 2 != 0) {
      cout << "NA";
      goto P;
    }
    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 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 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 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 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 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(' ');
      }
    }
  P:
    cout << endl;
  }
}
