#include <bits/stdc++.h>
using namespace std;
const long long N = 10e5 + 5;
const long long NN = 105;
const double pi = 3.14159;
const long long MAX = 2e5 + 123;
const long long MOD = 1e9 + 7;
const long long INF = 1000000000000000000;
const long long pw = 31;
void speed() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
}
void hajime() {
  string s;
  cin >> s;
  vector<long long> v(s.size() + 1);
  long long l = 0, r = 0;
  for (long long i = 1; i < s.size(); i++) {
    if (i <= r) v[i] = min(v[i - l], r - i + 1);
    while (i + v[i] < s.size() && s[i + v[i]] == s[v[i]]) v[i]++;
    if (i + v[i] - 1 > r) {
      l = i;
      r = i + v[i] - 1;
    }
    if (i + v[i] == s.size()) {
      for (long long j = i - 1; j > 0; j--) {
        if (v[j] >= v[i]) {
          for (int k = i; k < s.size(); k++) {
            cout << s[k];
          }
          return;
        }
      }
    }
  }
  cout << "Just a legend";
}
int main() {
  long long miyagl = 1;
  for (long long miyagi = 1; miyagi <= miyagl; miyagi++) {
    hajime();
  }
}
