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

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

#define _gp(l) const auto gcu{getchar##l}; const auto pcu{putchar##l}
#ifdef __linux
_gp(_unlocked);
#else
_gp();
#endif
#define _DEF(r, n, ...) inline r n(__VA_ARGS__) noexcept
#define _T template<typename T>
#define _HT template<typename H,typename... T>
_T _DEF(T,in,int c){T n{};int m{1};while(isspace(c)){c=gcu();}if(c=='-')m=-1,c=gcu();do{n=10*n+(c-'0'),c=gcu();}while(c>='0'&&c<='9');return m*n;}
_DEF(int,in,){return in<int>(gcu());}
#define _SCAN(...) _DEF(bool,scan,__VA_ARGS__)
_SCAN(char &c){c=gcu();gcu();return c!=EOF;}
_T _SCAN(T &n){int c{gcu()};return c==EOF?false:(n=in<T>(c),true);}
#define _OUT(...) _DEF(void,out,__VA_ARGS__)
#define _OUTL(...) _DEF(void,outl,__VA_ARGS__)
_OUT(bool b){pcu('0'+b);}
_OUT(char c){pcu(c);}
#ifdef _GLIBCXX_STRING
_SCAN(string &s){int c;s="";for(;;){c=gcu();if(c=='\n'||c==' ')return true;else if(c==EOF)return false;s+=(char)c;}}
_OUT(string s){for(char c:s)pcu(c);}
#endif
_OUT(const char *s){while(*s)pcu(*s++);}
_T _OUT(T n){static char b[20];char *p{b};T m=n<0?pcu('-'),-1:1;if(!n)*p++='0';else while(n)*p++=(char)(n%10*m+'0'),n/=10;while(p!=b)pcu(*--p);}
_OUTL(){out('\n');}
#ifdef _GLIBCXX_VECTOR
_T _OUT(vector<T> v){for(T &x:v)out(&x == &v[0]?"":" "),out(x);}
#endif
_HT _SCAN(H &h,T&&... t){return scan(h)&&scan(t...);}
_HT _OUT(H&& h, T&&... t){out(h);out(move(t)...);}
template <typename... T> _OUTL(T&&... t){out(move(t)...);outl();}
struct range{int e,b{0},s{1};range(int _b,int _e,int _s):e(_e),b(_b),s(_s){}range(int _b,int _e):e(_e),b(_b){}range(int _e):e(_e){}
	struct it{int v,s;it(int _v,int _s):v(_v),s(_s){}operator int()const{return v;}operator int&(){return v;}int operator*()const{return v;}it& operator++(){v+=s;return *this;}};
	it begin(){return{b, s};}it end(){return{e,s};}bool inner(int n){return b<=n&&n<e;}};

int main() {
	for (string a; scan(a);) {
		if (a.size() % 2) {
			outl("NA");
			continue;
		}
		string b;
		for (auto i {begin(a)}; i != end(a); i += 2) {
			int r = i[1] - '1', s {*i - '1'};
			if (!(range(5).inner(r) && range(6).inner(s))) {
				b = "NA";
				break;
			}
			int c {'a' + s * 5 + r};
			b.push_back(c > 'z' ? ".?! "[c - '{'] : c);
		}
		outl(b);
	}
}

C++: #include <bits/stdc++.h>
using namespace std;
#define FOR(i, s, n) for(int i = s; i < (int)n; i++)
#define per(i, n) for(int i = n; i >= 0; i--)
#define ROF(i, s, n) for(int i = s; i >= (int)n; i--)
#define FORIT(i, A) for (auto i : A)
#define PRINT(x) cout << (x) << "\n"
#define ALL(a) (a).begin(),(a).end()
#define RALL(a) (a).rbegin(), (a).rend()
#define MP make_pair
#define EACH(i, n) for (__typeof((n).begin()) i = (n).begin(); i != (n).end(); ++i)
#define SZ(a) int((a).size())
#define EXIST(s,e) ((s).find(e)!=(s).end())
#define SORT(c) sort((c).begin(),(c).end())
#define CLR(a) memset((a), 0 ,sizeof(a))
#define NCLR(a) memset((a), -1 ,sizeof(a))
#define dump(x) cout << #x << " = " << (x) << "\n";
#define debug(x) cout << #x << " = " << (x) << " (L" << __LINE__ << ")" << " " << __FILE__ << "\n";
#define sq(n) (n) * (n)
typedef vector<int> VI;
typedef vector<VI> VVI;
typedef vector<string> VS;
typedef pair<int, int> PII;
typedef long long LL;
typedef vector<LL> VLL;
typedef vector<VLL> VVLL;
typedef unsigned int uint;
typedef unsigned long long ull;
typedef priority_queue<int> maxpq;
typedef priority_queue< int, vector<int>, greater<int> > minpq;
typedef complex<double> P;
static const double EPS = 1e-10;
static const double PI = acos( -1.0 );
static const int mod = 1000000007;
static const int INF = 1 << 29;
static const LL LL_INF = 1152921504606846976;
static const int dx[] = { -1, 0, 1, 0, 1, -1, 1, -1 };
static const int dy[] = { 0, -1, 0, 1, 1, 1, -1, -1 };

char c[ 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 ) {
			printf( "NA\n" );
			continue;
		}
		string ans = "";
		for ( int i = 0; i < s.size(); i += 2 ) {
			if ( s[ i ] < '1' || '6' < s[ i ] || s[ i + 1 ] < '1' || '6' < s[ i + 1 ] ) {
				printf( "NA\n" );
				break;
			}
			ans += c[ s[ i ] - '1' ][ s[ i + 1 ] - '1' ];
		}
		if ( ans.size() != s.size() / 2 ) {
			continue;
		}
		printf( "%s\n", ans.c_str() );
	}
	return 0;
}

C++: #include <cstdio>
#include <cstring>
#include <algorithm>
#include <string>
#include <cmath>
#include <stack>
#include <vector>
#include <map>
#include <set>
#include <queue>
#include <list>
#include <iostream>
#include <sstream>
#include <climits>
#include <cfloat>

typedef long long ll;

using namespace std;

int main()
{
	char* table = "abcdefghijklmnopqrstuvwxyz.?! ";
	char buf[256];
	while (cin.getline(buf, sizeof(buf)), !feof(stdin) && strlen(buf))
	{
		if (strlen(buf) & 1)
		{
			puts("NA");
			continue;
		}

		char decode[128];
		memset(decode, 0, sizeof(decode));
		bool ok = true;
		for (int i = 0; buf[i] != '\0'; i += 2)
		{
			int c = buf[i] - '0' - 1;
			int r = buf[i+1] - '0' - 1;
			if (c > 5 || r > 5)
			{
				ok = false;
				break;
			}

			decode[i/2] = table[c*5 + r];
		}
		if (ok)
			puts(decode);
		else
			puts("NA");
	}

	return 0;
}