#include <bits/stdc++.h>
using namespace std;
const int N = 1e6 + 123;
const int mod = 1e9 + 8;
const int inf = 1e9 + 123;
const long long INF = 1e18 + 123;
const double eps = (double)(1e-9);
const double pi = 3.14159265358979323846264;
const int dx[] = {1, 1, 0, -1, -1, -1, 0, 1};
const int dy[] = {0, 1, 1, 1, 0, -1, -1, -1};
const pair<int, int> dir[] = {make_pair(-1, 0), make_pair(0, -1),
                              make_pair(1, 0), make_pair(0, 1)};
const pair<int, int> dirr[] = {
    make_pair(-2, 1), make_pair(1, -2), make_pair(2, -1),  make_pair(-1, 2),
    make_pair(2, 1),  make_pair(1, 2),  make_pair(-2, -1), make_pair(-1, -2)};
string second;
long long p[N], h[N], pr = 31;
string ans;
long long get(long long i, long long j) {
  return (h[j] - (h[i] * p[j - i]) % mod + mod) % mod;
}
bool check(long long len) {
  long long i = len;
  long long j = second.size() - len + 1;
  long long x = h[i];
  long long y = get(j - 1, second.size());
  if (x != y) {
    return 0;
  }
  bool ok = 0;
  for (long long k = len + 1; k < second.size(); ++k) {
    long long z = get(k - len, k);
    if (x == z && y == z) {
      ok = 1;
      break;
    }
  }
  if (!ok) {
    return 0;
  }
  ans = "";
  for (long long i = 1; i <= len; ++i) {
    ans += second[i - 1];
  }
  return 1;
}
int main() {
  cin.tie(0);
  cout.tie(0);
  cout.precision(0);
  ios_base::sync_with_stdio(0);
  cin >> second;
  p[0] = 1;
  for (long long i = 1; i <= 1e6; ++i) {
    p[i] = (p[i - 1] * pr) % mod;
  }
  for (long long i = 1; i <= second.size(); ++i) {
    h[i] = (h[i - 1] * pr + second[i - 1]) % mod;
  }
  for (long long i = second.size(); i > 0; --i) {
    if (check(i)) {
      break;
    }
  }
  if (!ans.size()) {
    cout << "Just a legend";
    return 0;
  }
  cout << ans;
  return 0;
}
