#include <bits/stdc++.h>
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;
  }
}
