#include <bits/stdc++.h>
int main() {
  char str[250], ans[250],
      tmp[10][10] = {"abcde", "fghij", "klmno", "pqrst", "uvwxy", "z.?! "};
  int i, flg, l, a, cnt;
  while (scanf("%s", str) != EOF) {
    for (i = 0; i < 240; i++) ans[i] = 0;
    l = strlen(str);
    if (l % 2 == 1)
      printf("NA\n");
    else {
      for (cnt = 0, i = 0; i < l; i += 2, cnt++) {
        ans[cnt] = tmp[(str[i] - '0' - 1)][(str[i + 1] - '0' - 1)];
      }
      str[cnt + 1] = '\0';
      printf("%s\n", ans);
    }
  }
  return 0;
}
