Go: package main

import (
	"bufio"
	"os"
	"strings"
	"fmt"
		"strconv"
	)

var scanner = bufio.NewScanner(os.Stdin)

func main() {
	table := [6][5]string{
		{"a", "b", "c", "d", "e"},
		{"f", "g", "h", "i", "j"},
		{"k", "l", "m", "n", "o"},
		{"p", "q", "r", "s", "t"},
		{"u", "v", "w", "x", "y"},
		{"z", ".", "?", "!", " "},
	}
	for scanner.Scan() {
		input := strings.Split(scanner.Text(), "")
		if len(input) % 2 != 0 {
			fmt.Println("NA")
			continue
		}
		ret := make([]string, 0)
		for i := 0; i < len(input); i += 2 {
			row, _ := strconv.Atoi(input[i])
			col, _ := strconv.Atoi(input[i+1])
			// log.Println(table[row-1][col-1])
			ret = append(ret, table[row-1][col-1])
		}
		fmt.Println(strings.Join(ret, ""))
	}
}

C++: #include <iostream>
#include <algorithm>
#include <cassert>
#include <cctype>
#include <complex>
#include <cstdio>
#include <map>
#include <math.h>
#include <queue>
#include <set>
#include <stack>
#include <string>
#include <vector>
using namespace std;

char c[]={'z','.','?','!',' '};
string s;

int main(){
	while(getline(cin,s)){
		int l=s.size();
		if(l%2){cout<<"NA"<<endl;continue;}
		int cur=0,f=0;
		string ans="";
		while(cur<l){
			int a=s[cur++]-'0',b=s[cur++]-'0';
			if(a<1||a>6||b<1||b>5){cout<<"NA"<<endl;f=1;break;}
			if(a<6)ans+=(char)('a'+(a-1)*5+b-1);
			if(a==6)ans+=c[b-1];
		}
		if(!f)cout<<ans<<endl;
	}
}

C++: #include<iostream>
using namespace std;
int main(){
char g[] = {97,102,107,112,117,122,98,103,108,113,118,46,99,104,109,114,119,63,100,105,110,115,120,33,101,106,111,116,121,32};
string s,a;
while(cin>>s,!cin.eof()){
a = "";
for(int i = 0;i < s.size();i += 2){
int l = s[i] - '0', r = s[i+1] - '0';
if(s.size() % 2 || l < 1 || r < 1 || l > 6 || r > 5){a = "NA";break;}
a += g[r * 6 + l - 7];
}
cout << a << '\n';
}	
}

C++: #include<cstdio>
#include<cstring>
using namespace std;
int main(){
    char a[7][7] = {"","*abcde","*fghij","*klmno","*pqrst","*uvwxy","*z.?! "};
    char s[200];
    while(~scanf("%s",s)){
        bool flg = false;
        if(strlen(s)%2==1)flg = true;
        else{
            for(int i=0;i<strlen(s);i++){
                if(s[i]<49||s[i]>54){
                    flg = true;
                    break;
                }
            }
            for(int i=0;i<strlen(s);i+=2){
                printf("%c",a[s[i]-48][s[i+1]-48]);
            }
            printf("\n");
        }
        if(flg)printf("NA\n");
    }
    return 0;
}

C++: #include <cstdio>
#include <cstdlib>
#include <cstring>
char buf[256], res[256];
char* s = "z.?! ";
int main()
{
    while (fgets(buf, 256, stdin)) {
        int k = 0;
        bool ok = true;
        for (int i = 0; i < strlen(buf)-1; i+=2) {
            if ('1' <= buf[i] && buf[i] <= '5') {
                if ('1' <= buf[i+1] && buf[i+1] <= '5')
                    res[k++] = 'a' + 5 * (buf[i]-'1') + (buf[i+1]-'1');
                else ok = false;
            }
            else if (buf[i] == '6' && '1' <= buf[i+1] && buf[i+1] <= '5') {
                res[k++] = s[buf[i+1]-'1'];
            }
            else {
                ok = false;
            }
        }
        res[k] = '\0';
        if (ok) puts(res); else puts("NA");
    }
    return 0;
}

C++: #include <iostream>
#include <string>
#include <vector>
#include <algorithm>
#include <cmath>
#include <cstdio>
#include <functional>
#include <numeric>
#include <stack>
#include <queue>
#include <map>
#include <set>
#include <utility>
#include <sstream>
#include <complex>

using namespace std;

#define FOR(i,a,b) for(long long i=(a);i<(b);i++)
#define REP(i,N) for(long long i=0;i<(N);i++)
#define ALL(s) (s).begin(),(s).end()
#define fi first
#define se second

#define PI acos(-1.0)
#define INF 1000000007

typedef long long ll;
typedef pair<ll, ll> P;
typedef pair<double, double> PD;
typedef pair<string, ll> PS;
typedef vector<ll> V;

string ans, s;
char table[6][8] = { "@@@@@@@", "@afkpuz", "@bglqv.", 
"@chmrw?", "@dinsx!", "@ejoty " };

int main(){
	while (cin >> s){
		bool f = 0;
		ans = "";
		if (s.size() % 2 != 0){
			cout << "NA" << endl;
			continue;
		}
		if (s.size() == 0)cout << "NA" << endl;
		for (int i = 0; i < s.size(); i += 2){
			if (s[i]>'6' || s[i]<'0' || s[i + 1]>'6' || s[i] < '0')f = 1;
			ans += table[s[i + 1] - '0'][s[i] - '0'];
		}
		if (f)cout << "NA" << endl;
		else cout << ans << endl;
	}
}

C++: #include <cstdio>
#include <cstdlib>
#include <cmath>
#include <climits>
#include <cfloat>
#include <cstring>
#include <map>
#include <utility>
#include <set>
#include <iostream>
#include <memory>
#include <string>
#include <vector>
#include <algorithm>
#include <functional>
#include <sstream>
#include <fstream>
#include <complex>
#include <stack>
#include <queue>

using namespace std;
typedef long long LL;
typedef pair<int, int> PII;
static const double EPS = 1e-5;

#define FOR(i,k,n) for (int i=(k); i<(int)(n); ++i)
#define REP(i,n) FOR(i,0,n)
string a = "afkpu";
int main(void){
  string line;
  while(cin>>line){
    string ans;
    bool na = false;
    if(line.size()%2){
      na = true;
    }
    for(int i=0;i<(int)line.size(); i+=2){
      if(na) break;
      if(line[i+1]>='7'||line[i+1]<='0'){
        na = true;
        break;
      }
      if(line[i]<='5'){
        ans+=(char)(a[line[i]-'1']+line[i+1]-'1');
      }else if(line[i]=='6'){
        if(line[i+1]=='1') ans+='z';
        if(line[i+1]=='2') ans+='.';
        if(line[i+1]=='3') ans+='?';
        if(line[i+1]=='4') ans+='!';
        if(line[i+1]=='5') ans+=' ';
      }else{
        na = true;
        break;
      }
    }
    if(!na)cout<<ans<<endl;
    else cout<<"NA"<<endl;
  }
  return 0;
}

C++: #define _CRT_SECURE_NO_WARNINGS
#define _USE_MATH_DEFINES

#include <stdio.h>
#include <ctype.h>
#include <string>
#include <iostream>
#include <vector>
#include <stack>
#include <fstream>
#include <sstream>
#include <queue>
#include <exception>
#include <cmath>
#include <numeric>
#include <map>
#include <algorithm>
#include <bitset>
#include <set>
#include <functional>

#define FOR(i,a,b) for (int i=(a);i<(b);i++)
#define RFOR(i,a,b) for (int i=(b)-1;i>=(a);i--)
#define REP(i,n) for (int i=0;i<(n);i++)
#define RREP(i,n) for (int i=(n)-1;i>=0;i--)

using namespace std;
typedef long long int lint;

vector<string> keys;
vector<char> vals;
map<string, char> encoder;

bool AOJ0127()
{
	string str, ret;
	cin >> str;

	if (str.size() % 2) {
		cout << "NA" << endl;
		return true;
	}

	REP(i, str.size() / 2) {
		string buf = str.substr(2 * i, 2);
		if (encoder.find(buf) == encoder.end()) {
			cout << "NA" << endl;
			return true;
		}
		ret.push_back(encoder[buf]);
	}
	cout << ret << endl;

	return true;
}

int main()
{
	FOR(i, 1, 7) {
		FOR(j, 1, 6) {
			string key;
			key.push_back('0' + i);
			key.push_back('0' + j);
			keys.push_back(key);
		}
	}

	for (char c = 'a'; c <= 'z'; c++) {
		vals.push_back(c);
	}
	vals.push_back('.');
	vals.push_back('?');
	vals.push_back('!');
	vals.push_back(' ');

	REP(i, keys.size()) {
		encoder[keys[i]] = vals[i];
	}

	while (AOJ0127()) {

	}

	return 0;
}