#include <bits/stdc++.h>
using namespace std;
string s;
long long int p = 31, flag;
long long int hash_prefix[1000001];
long long int pw[1000000];
const long long int MOD = 1e9 + 9;
long long int pf, ppf, sf, tf, best = -1;
int main() {
  cin >> s;
  pw[0] = 1;
  for (int i = 1; i < 1000000; i++) {
    pw[i] = (pw[i - 1] % MOD * p) % MOD;
  }
  for (int i = 0; s[i]; i++) {
    hash_prefix[i] = ((s[i] - 'a' + 1) * pw[i]) % MOD;
  }
  for (int i = 1; s[i]; i++) {
    hash_prefix[i] += hash_prefix[i - 1];
    hash_prefix[i] %= MOD;
  }
  for (int ln = s.length() - 1; ln > 0; ln--) {
    pf = hash_prefix[ln - 1];
    ppf = (pf * pw[s.length() - ln]) % MOD;
    sf = hash_prefix[s.length() - 1] - hash_prefix[s.length() - ln - 1];
    if (sf < 0) sf += MOD;
    if (sf == ppf) {
      flag = 0;
      for (int i = 1; i + ln - 1 < s.length() - 1; i++) {
        tf = hash_prefix[i + ln - 1] - hash_prefix[i - 1];
        if (tf < 0) tf += MOD;
        ppf = (pf * pw[i]) % MOD;
        if (ppf == tf) flag = 1;
      }
      if (flag) {
        best = ln;
        break;
      }
    }
  }
  if (best == -1) {
    cout << "Just a legend" << '\n';
  } else {
    for (int i = 0; i < best; i++) cout << s[i];
  }
  return 0;
}
