#include <iostream>
#include <string>
#include <cstdio>
#include <cstdlib>
using namespace std;
int main(){
	int sum,x;
	string str;
	char abc[31]={"abcdefghijklmnopqrstuvwxyz.?! "};
	while(cin>>str){
		string ans="";
		int num=0;
		x=str.size();
		if(x%2!=0)cout<<"NA"<<endl;
		else{
			for(int i=0;i<x;i++){
				char c=str[i];
				if(i%2==1){
					if((int)(c-'0')>5){num++;break;}
					sum=sum+(int)(c-'0');
					ans+=abc[sum];
				}else{
					if((int)(c-'0')>6){num++;break;}
					sum=(int)(c-'0');
					sum=(sum-1)*5-1;
				}
			}
			if(num==0){
				cout<<ans<<endl;
			}else{
				cout<<"NA"<<endl;
			}
		}
	}
	return 0;
}