#include <bits/stdc++.h>
using namespace std;
const int INF = 0x3f3f3f3f;
const long long LINF = 0x3f3f3f3f3f3f3f3fll;
mt19937 rng((int)chrono::steady_clock::now().time_since_epoch().count());
int uniform(int l, int r) {
  uniform_int_distribution<int> uid(l, r);
  return uid(rng);
}
template <int MOD>
struct str_hash {
  static int P;
  int n;
  string second;
  vector<long long> h, power;
  str_hash(string s_) : n(s_.size()), second(s_), h(n), power(n) {
    power[0] = 1;
    for (int i = 1; i < n; i++) power[i] = power[i - 1] * P % MOD;
    h[0] = second[0];
    for (int i = 1; i < n; i++) h[i] = (h[i - 1] * P + second[i]) % MOD;
  }
  long long operator()(int i, int j) {
    if (!i) return h[j];
    long long ret = h[j] - h[i - 1] * power[j - i + 1] % MOD;
    return ret < 0 ? ret + MOD : ret;
  }
};
template <int MOD>
int str_hash<MOD>::P = uniform(27, MOD - 1);
const int MOD = 1e9 + 7;
int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  string second;
  cin >> second;
  str_hash<MOD> h(second);
  vector<pair<int, int> > pos;
  for (int i = 0; i < second.size() - 1; i++) {
    int a = h(0, i), b = h(second.size() - 1 - i, second.size() - 1);
    if (a == b) pos.push_back({i, a});
  }
  reverse(pos.begin(), pos.end());
  int ans = -1;
  for (auto p : pos) {
    for (int j = 1; j < second.size() - 1 - p.first; j++) {
      if (h(j, j + p.first) == p.second) {
        ans = p.first;
        break;
      }
    }
    if (ans != -1) break;
  }
  if (ans == -1)
    cout << "Just a legend" << '\n';
  else {
    for (int i = 0; i <= ans; i++) cout << second[i];
    cout << '\n';
  }
  exit(0);
}
