#include <iostream>
using namespace std;
 
char *end  (char *p) {return *p ? end(p+1) : p-1;}
int length (char *p) {return *p ? 1+length(p+1) : 0;}
bool ispal (char *b, char *e) {return b>=e ? true : *b==*e && ispal (b+1, e-1);}
void strcp (char *s, char *r) {if (*s) {*r=*s; strcp(s+1, r+1);} else *r=0;}
void test  (char *s, char *r) {if (ispal(s, end(s)) && length(s)>length(r)) strcp(s, r);}
 
int main() {char s[100], r[100]=""; while (cin>>s) test(s,r); cout<<(*r ? r : "отсутствует"); return 0;}

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