#include <bits/stdc++.h>
using namespace std;
string s;
vector<string> vec;
int main()
{
    cin >> s;
    for (int n = s.length() - 1; n >= 1; n--)
    {
        bool flag = false;
        vec.clear();
        for (int i = 0; i + n - 1 < s.length(); i++)
            vec.push_back(s.substr(i, n));
        sort(vec.begin(), vec.end());
        int sz = vec.size();
        for (int i = 0; i + 1 < sz; i++)
        {
            if (vec[i] == vec[i+1])
            {
                cout << vec[i] << endl;
                return 0;
            }
        }
    }
    puts("So Sad!");
    return 0;
}