#include <bits/stdc++.h>
using namespace std;
const int p = 31;
vector<long long> p_pow;
vector<long long> h;
long long get_h(int i1, int len) {
  long long h1 = h[i1 + len - 1];
  if (i1) h1 -= h[i1 - 1];
  return h1;
}
string s;
bool check(int n) {
  if (get_h(0, n) * p_pow[s.length() - 1 - n] != get_h(s.length() - n, n))
    return false;
  for (int i = 1; i < s.length() - n; i++)
    if (get_h(i, n) == get_h(0, n) * p_pow[i - 1]) return true;
  return false;
}
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(0);
  cout.tie(0);
  cin >> s;
  p_pow.resize(s.length() + 1);
  h.resize(s.length());
  p_pow[0] = p;
  for (int i = 1; i < s.length(); i++) p_pow[i] = p * p_pow[i - 1];
  for (int i = 0; i < s.length(); i++) {
    h[i] = (s[i] - 'a' + 1) * p_pow[i];
    if (i) h[i] += h[i - 1];
  }
  for (int i = s.length() - 2; i > 0; i--) {
    if (check(i)) {
      string res = "";
      for (int j = 0; j < i; j++) res += s[j];
      cout << res;
      return 0;
    }
  }
  cout << "Just a legend";
}
