#include <bits/stdc++.h>
using namespace std;
template <class T>
void chmin(T &t, T f) {
  if (t > f) t = f;
}
template <class T>
void chmax(T &t, T f) {
  if (t < f) t = f;
}
template <typename T>
T gcd(T a, T b) {
  return b ? gcd(b, a % b) : a;
}
template <typename T>
T sqr(T x) {
  return x * x;
}
template <typename T>
T cube(T x) {
  return x * x * x;
}
string out(long long x) {
  stringstream ss;
  ss << x;
  string res;
  ss >> res;
  return res;
}
long long out(string s) {
  stringstream ss;
  ss << s;
  long long res;
  ss >> res;
  return res;
}
long long fact(int n) { return n ? n * fact(n - 1) : 1; }
template <typename T>
void print(const vector<vector<T> > &v) {
  for (int i = 0; i < (int)(v.size()); i++) {
    cout << "i = " << i << endl;
    for (int j = 0; j < (int)(v[i].size()); j++) {
      cout << v[i][j] << ' ';
    }
    cout << endl;
    cout << endl;
  }
}
template <typename T>
void print(const vector<T> &v) {
  for (int i = 0; i < (int)(v.size()); i++) {
    cout << v[i] << ' ';
  }
  cout << endl;
}
int t1, t2, x1, x2, t0;
long long func(long long y1, long long y2) {
  return (t1 * y1 + t2 * y2) - t0 * (y1 + y2);
}
vector<int> z_function(string s) {
  int n = (int)s.length();
  vector<int> z(n);
  for (int i = 1, l = 0, r = 0; i < n; ++i) {
    if (i <= r) z[i] = min(r - i + 1, z[i - l]);
    while (i + z[i] < n && s[z[i]] == s[i + z[i]]) ++z[i];
    if (i + z[i] - 1 > r) l = i, r = i + z[i] - 1;
  }
  return z;
}
void no() {
  cout << "Just a legend" << endl;
  exit(0);
}
int main() {
  string s;
  cin >> s;
  vector<int> z = z_function(s);
  set<int> maxMiddle;
  int n = s.size();
  for (int i = 1; i < n; i++) {
    maxMiddle.insert(min(z[i], n - i - 1));
  }
  maxMiddle.erase(0);
  set<int> resSize;
  for (int i = z.size() - 1; i; i--) {
    int tmp = n - i;
    if (z[i] == tmp) {
      resSize.insert(tmp);
    }
  }
  resSize.erase(0);
  vector<int> mm(maxMiddle.begin(), maxMiddle.end());
  vector<int> sp(resSize.begin(), resSize.end());
  for (int i = (int)(sp.size()) - 1; i >= 0; i--) {
    if (lower_bound(mm.begin(), mm.end(), sp[i]) != mm.end()) {
      cout << s.substr(0, sp[i]) << endl;
      return 0;
    }
  }
  no();
  return 0;
}
