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

void find_palindrome(const char *);
int is_palindrome(const char *, int);
const char *find_last_char(const char *, char, int);

void find_palindrome(const char *text) {
	int i;
	int psize;
	const char *ith;
	const char *hit;
	unsigned int textlen = strlen(text);
	for ( i = 0; text[i] != '\0'; i++ ) {
		if ( !isalnum(text[i]) ) {
			continue;
		}
		ith = &text[i];
		hit = find_last_char( ith + 1, *ith, textlen - i - 1 );
		while ( hit != NULL ) {
			psize = hit - ith + 1;
			if ( is_palindrome(ith, psize) ) {
				while ( ith < hit + 1 ) {
					putchar(*ith);
					ith++;
				}
				putchar('\n');
				return;
			}
			hit = find_last_char( ith + 1, *ith, psize - 2 );
		}
	}
}
int is_palindrome(const char *chars, int size) {
	int l;
	int r;
	for ( l = 0, r = size - 1; l < r; l++, r-- ) {
		while ( !isalnum(chars[l]) ) {
			l++;
		}
		while ( !isalnum(chars[r]) ) {
			r--;
		}
		if ( tolower( chars[l] ) != tolower( chars[r] ) ) {
			return 0;
		}
	}
	return 1;
}
const char *find_last_char(const char *str, char ch, int count){
	int i;
	for ( i = count -1; i >= 0; i-- ) {
		if ( tolower( ch ) == tolower( str[i] ) ) {
			return &str[i];
		}
	}
	return NULL;
}

int main(int argc, const char **argv) {
	if ( argc <= 1 ) {
		fprintf(stderr, "USAGE:%s string\n", argv[0]);
		return 1;
	}
	find_palindrome(argv[1]);
	return 0;
}