Go: package main

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

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])
			ret = append(ret, table[row-1][col-1])
		}
		fmt.Println(strings.Join(ret, ""))
	}
}

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;
}

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]>='6'||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++: #include<bits/stdc++.h>
using namespace std;
int main(){
  string str[6]={"afkpuz","bglqv.","chmrw?"
		 ,"dinsx!","ejoty "};
  string str2;
  while(cin>>str2){
    if(str2.size()%2==1)
      cout<<"NA"<<endl;
    else{
      string ans="";
      for(int i=0;i<str2.size();i+=2){
	if(str2[i+1]-'0'<=5&&str2[i]-'0'<=6&&str2[i+1]-'0'>0&&str2[i]-'0'>0){
	ans+=str[str2[i+1]-'0'-1][str2[i]-'0'-1];
	}
	else{
	  ans="NA";
	}
      }
      cout<<ans<<endl;
    }
  }
  return 0;
}

C++: #include <iostream>
#include <cstdio>
#include <string>
using namespace std;

int index[6][5] {
  {'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', '.', '?', '!', ' '},
};

int main() {
  string s;
  while(cin >> s) {
    if(s.size()%2) cout << "NA" << endl;
    else {
      string ans;
      for(int i = 0; i < s.size(); i += 2) {
        int column = s[i]-'1', row = s[i+1]-'1';
        if(column > 5 || row > 4) {
          cout << "NA" << endl;
          break;
        }
        ans += index[column][row];
        if(i+2 == s.size()) cout << ans << endl;
      }
    }
  }
}

C++: #include<iostream>
#include<string>
using namespace std;
int main(){
  string str;
  char hyou[6][7];
  hyou[1][6] = 'z';
  hyou[2][6] = '.';
  hyou[3][6] = '?';
  hyou[4][6] = '!';
  hyou[5][6] = ' ';
  for(int i=1;i<=5;i++){
    for(int j=1;j<=5;j++){
      hyou[i][j] = 'a'+(j-1)*5+i-1;
    }
  }
  
  while(cin >> str){
    if(str.size()%2 != 0){
      cout << "NA" << endl;
      continue;
    }
    for(int i=0;i<str.size();i+=2){
      cout << hyou[ str[i+1]-'0'][str[i]-'0'];
    } cout << endl;
  }

  return (0);
}