#include <bits/stdc++.h>
using namespace std;
char s[6][6] = {"abcde", "fghij", "klmno", "pqrst", "uvwxy", "z.?! "};
int main(void) {
  string str;
  while (cin >> str) {
    if (str.length() % 2 == 1) {
      cout << "NA\n";
      continue;
    }
    string ans = "";
    bool flg = false;
    for (int i = 0; i < str.length(); i += 2) {
      if ('1' > str[i] || str[i] >= '7' || '1' > str[i + 1] ||
          str[i + 1] >= '7') {
        cout << "NA\n";
        flg = true;
        break;
      }
      int a = str[i] - '1';
      int b = str[i + 1] - '1';
      ans += s[a][b];
    }
    if (flg) continue;
    cout << ans << endl;
  }
  return 0;
}
