#include <bits/stdc++.h>
using namespace std;
using ull = unsigned long long;
const int maxn = 1e6 + 10;
const ull p = 701, mod = 1e9 + 7;
string s;
int n;
ull h[maxn], po[maxn];
vector<int> v;
bool check(int x) {
  for (int i = x; i < n - 1; i++)
    if ((h[x - 1] * po[i - x + 1] % mod) == ((mod + h[i] - h[i - x]) % mod))
      return true;
  return false;
}
int main() {
  ios_base::sync_with_stdio(0), cin.tie(0), cout.tie(0);
  cin >> s;
  n = s.size();
  po[0] = 1;
  for (int i = 1; i < maxn; i++) po[i] = (po[i - 1] * p) % mod;
  h[0] = s[0] - 'a' + 1;
  for (int i = 1; i < n; i++)
    h[i] = (h[i - 1] + (((s[i] - 'a' + 1) * po[i]) % mod)) % mod;
  for (int i = 1; i < n; i++)
    if ((h[i - 1] * po[n - i] % mod) == ((mod + h[n - 1] - h[n - i - 1]) % mod))
      v.push_back(i);
  if (v.empty() || !check(v[0])) {
    cout << "Just a legend\n";
    return 0;
  }
  int l = 0, r = v.size();
  while (l + 1 < r) {
    int mid = (l + r) / 2;
    if (check(v[mid]))
      l = mid;
    else
      r = mid;
  }
  for (int i = 0; i < v[l]; i++) cout << s[i];
  cout << "\n";
  return 0;
}
