#include<iostream>
#include<iomanip>
#include<algorithm>
#include<array>
#include<bitset>
#include<cassert>
#include<cctype>
#include<cmath>
#include<cstdio>
#include<cstring>
#include<functional>
#include<limits>
#include<list>
#include<map>
#include<numeric>
#include<set>
#include<stack>
#include<string>
#include<sstream>
#include<unordered_map>
#include<queue>
#include<vector>
using namespace std;

//#define int long long
using ll = long long;
using ull = unsigned long long;
using pii = pair<int, int>;

#define rep(i,a,b) for(int i=(a);i<(b);i++)
#define rrep(i,a,b) for(int i=(b)-1;i>=(a);i--)
#define all(a) (a).begin(),(a).end()
#define dump(o) {cerr<<#o<<" "<<o<<endl;}
#define dumpc(o) {cerr<<#o; for(auto &e:(o))cerr<<" "<<e;cerr<<endl;}
#define INF 0x3f3f3f3f
#define INFL 0x3f3f3f3f3f3f3f3fLL
const int MOD = 1e9 + 7;

signed main() {
	string A[] = { "abcde","fghij","klmno","pqrst","uvwxy","z.?! " };
	for (string s; cin >> s;) {
		if (s.size() % 2) {
			cout << "NA" << endl;
			continue;
		}
		bool flag = false;
		string ans = "";
		for (int i = 0; i < s.size(); i += 2) {
			if (!('1' <= s[i] && s[i] <= '6' && '1' <= s[i + 1] && s[i + 1] <= '5')) {
				cout << "NA" << endl;
				flag = true;
				break;
			}
			ans += A[s[i] - '1'][s[i + 1] - '1'];
		}
		if (flag) {
			continue;
		}
		cout << ans << endl;
	}
	return 0;
}