#include<iostream>
#include<string.h>
using namespace std;
string a;
char calc(char s)
{
	if(s>=97)
		s-=32;
	return s;
}
bool flag(char s)
{
	if((s>='a'&&s<='z')||(s>='A'&&s<='Z')) return true;
	return false;
}
int main()
{
	getline(cin,a);
	int len=a.size();
	int l=0,r=0;
	int maxx=0;
	for(int i=0;i<len;i++)
	{
		if(flag(a[i]))
		{
			for(int j=i+1;j<len;j++)
			{
				if(calc(a[i])==calc(a[j]))
				{
					int idl=i,idr=j;
					while(idl<=idr)
					{
						char ls,rs;
						ls=calc(a[idl]);
						rs=calc(a[idr]);
						if(ls!=rs||!flag(ls)) break;
						idl++;
						while(!flag(a[idl])&&idl<=idr) idl++;
						idr--;
						while(!flag(a[idr])&&idl<=idr) idr--;
					}
					if(idl>idr&&maxx<j-i+1)
					{
						maxx=j-i+1;
						l=i,r=j;
					}
				}
			}
		}
	}
	for(int i=l;i<=r;i++) cout<<a[i];
	return 0;
}

#include<bits/stdc++.h> using namespace std; string a; char calc(char s) { if(s>=97) s-=32; return s; } bool flag(char s) { if((s>='a'&&s<='z')||(s>='A'&&s<='Z')) return true; return false; } int main() { getline(cin,a); int len=a.size(); int l=0,r=0; int maxx=0; for(int i=0;i<len;i++) { if(flag(a[i])) { for(int j=i+1;j<len;j++) { if(calc(a[i])==calc(a[j])) { int idl=i,idr=j; while(idl<=idr) { char ls,rs; ls=calc(a[idl]); rs=calc(a[idr]); if(ls!=rs||!flag(ls)) break; idl++; while(!flag(a[idl])&&idl<=idr) idl++; idr--; while(!flag(a[idr])&&idl<=idr) idr--; } if(idl>idr&&maxx<j-i+1) { maxx=j-i+1; l=i,r=j; } } } } } for(int i=l;i<=r;i++) cout<<a[i]; return 0; }