#include <string.h>
#include <stdio.h>

char s[200100];
char addC;
int addPos;
int saiki( int st, int gt, int rewrite ){
	int ret;
	if( st >= gt ){
		return 1;
	} 
	
	for(;s[st] == '\0';st++);
	for(;s[gt] == '\0';gt--);
	
	if( s[st] != s[gt]){
		if(rewrite != 0){
			return 0;
		}
		rewrite = 1;
		addC = s[st];
		addPos = gt+1;
		ret = saiki(st+1, gt, rewrite);
		if(ret == 0){
			addC = s[gt];
			addPos = st-1;
			ret = saiki(st, gt-1, rewrite);
		}
	}else{
		ret = saiki(st+1, gt-1, rewrite);
	}
	
	return ret;
}

int searchReverse( int st, int gt ){
	
	while(st < gt ){
		for(;s[st] == '\0';st++);
		for(;s[gt] == '\0';gt--);
		if( s[st] != s[gt]){
			return 0;
		}
		st+=1;
		gt-=1;
	}
	return st;
}

int main(void){
	char tmp[100100];
	int i, st=0, gt;
	int ret;
	
	fgets(tmp, sizeof(tmp), stdin);
	tmp[strlen(tmp)-1] = '\0';
	
	for(i=0;tmp[i] != '\0';i++){
		s[(i*2)+1] = tmp[i];
		gt = (i*2)+2;
	}
	
	ret = searchReverse(st,gt);
	if(ret != 0){
		addC = 'a';
		addPos = ret;
		ret = 1;
	}else{
		ret = saiki(st, gt, 0);
	}
	if(ret == 1){
		s[addPos] = addC;
		for(i=0;i<gt+1;i++){
			if(s[i] != '\0'){
				printf("%c", s[i]);
			}
		}
		printf("\n");
	}else{
		printf("NA\n");
	}
	return 0;
}