#include <iostream>
#include <string>

using namespace std;
string v;
int st,dr,i,j,n;
int main()
{
    cout<<"v=";cin>>v;
    for (i=1;i<=v.size();i++)
             {
                 st=i-1;
                 dr=v.size()+1;
                 while ((v[st]!=v[dr]) || (st==dr))
                       {
                          st=st+1;
                          dr=dr-1;
                       }
                if (st==dr)
                 {
                     j=i-1;
                     break;

                 }

             }
    for (i=st;i<=dr;i++)
        cout<<v[i];
    return 0;
}