#include <bits/stdc++.h>
using namespace std;
long long exp(long long a, long long p) {
  long long result = 1;
  if (p == 0) return 1;
  if (p == 1) return a;
  while (p) {
    if (p & 1) result *= a;
    p >>= 1;
    a *= a;
  }
  return result;
}
struct RH {
  vector<long long> rh;
  RH(string &s) {
    int N = s.length();
    rh.resize(N + 1, 0);
    rh[N] = 0;
    rh[N - 1] = s[N - 1];
    for (int i = N - 2; i >= 0; i--) {
      rh[i] = s[i] + rh[i + 1] * 33;
    }
  }
  long long getHash(int i, int len) {
    return rh[i] - rh[i + len] * exp(33, len);
  }
};
int main() {
  string s;
  cin >> s;
  RH rh = RH(s);
  int len = s.length();
  int l = len;
  bool flag = false;
  long long h;
  while (!flag) {
    h = rh.getHash(0, l);
    if (h == rh.getHash(len - l, l)) {
      for (int i = 1; i < len - l; i++) {
        if (h == rh.getHash(i, l)) {
          flag = true;
          break;
        }
      }
      if (!flag) l--;
    } else {
      l--;
    }
    if (l == 0) {
      cout << "Just a legend" << endl;
      return 0;
    }
  }
  cout << s.substr(0, l) << endl;
  return 0;
}
