#include <iostream>
#include <cstring>
using namespace std;

int main()
{
    char s[256],v[]="aeiou";
    cin.getline(s,256);
    int lmax=0,pmax;
    for(int i=0;i<strlen(s)-1;++i)
    {
        for(int j=i+1;j<strlen(s);++j)
            if(s[i]==s[j])
        {
            int pi=i;
            int pj=j;
            while(s[pi]==s[pj] and s[pi]!=NULL and s[pj]!=NULL)
            {
                pi++;
                pj++;
            }
            int l=pi-i;
            if(l>lmax)
                {
                    lmax=l;
                    pmax=i;
                }
            else
            if(l==lmax)
            {
                if(s[pmax]>s[i])
                    pmax=i;
                else
                if(s[i]==s[pmax])
                {
                    int i1=pmax;
                    int i2=i;
                    while(s[i1]==s[i2] and s[i1]!=NULL and s[i2]!=NULL)
                    {
                        i1++;
                        i2++;
                        if(s[i1]>s[i2])
                            pmax=i;
                    }
                }
            }
        }
    }
    for(int i=pmax;i<pmax+lmax;++i)
        cout<<s[i];
    return 0;
}