# include <fstream.h>
# include <string.h>
ifstream fin("rv.in");
ofstream fout("rv.out");
char a[102];
int n,i,st,dr;
int main()
{
 fin.getline(a,100);
 i=strlen(a);
 dr=i-1;
 st=0;
 while(st<dr)
     {
     if(a[st]>a[dr])
	fout<<a[st],st++;
	else
	fout<<a[dr],dr--;

     if(a[st]<a[dr])
	fout<<a[st],st++;
	else
	fout<<a[dr],dr--;
    }
 if(i%2!=0)
   fout<<a[st]<<'\n';
   else
   fout<<'\n';

fin.close();
fout.close();
return 0;
}