#include <bits/stdc++.h>
using namespace std;
const double PI = 3.14159265358979323846;
const double SQRT2 = 1.41421356237;
const double EPS = 1e-9;
const float SQRT2F = (float)SQRT2;
const int INF = 1e9;
const long long INF64 = 1e18;
template <class T>
T sqr(const T &x) {
  return x * x;
}
template <class T>
T min(const T &a, const T &b, const T &c) {
  return min(min(a, b), c);
}
template <class T>
T max(const T &a, const T &b, const T &c) {
  return max(max(a, b), c);
}
inline void yesno(bool y) { cout << (y ? "YES\n" : "NO\n"); }
inline void yes_stop(bool y) {
  if (y) {
    yesno(1);
    exit(0);
  }
}
inline void no_stop(bool y) {
  if (!y) {
    yesno(0);
    exit(0);
  }
}
int gcd(int a, int b) { return b ? gcd(b, a % b) : a; }
long long gcd(long long a, long long b) { return b ? gcd(b, a % b) : a; }
int sgn(int x) { return (x > 0) - (x < 0); }
class IManip {
 public:
  virtual void write(ostream &os) const {}
};
template <class It>
class ManipRangePrinter : public IManip {
 private:
  const It b, e;

 public:
  ManipRangePrinter(It _b, It _e) : b(_b), e(_e) {}
  void write(ostream &os) const {
    It g = b;
    if (g != e) os << *g;
    for (++g; g != e; ++g) {
      os << " " << *g;
    }
  }
  It begin() { return b; }
  It end() { return e; }
};
ostream &operator<<(ostream &os, const IManip &man) {
  man.write(os);
  return os;
}
template <class It>
ManipRangePrinter<It> range(It b, It e) {
  return ManipRangePrinter<It>(b, e);
}
struct Edge {
  int to, w;
  bool operator<(const Edge &x) const {
    if (to == x.to) return w < x.w;
    return to < x.to;
  }
};
void pref_func(const char *s, int *a) {
  a[0] = 0;
  for (int i = 1; s[i]; ++i) {
    int j = a[i - 1];
    while (j > 0 && s[i] != s[j]) j = a[j - 1];
    a[i] = j + (s[i] == s[j]);
  }
}
char s[(int)1e7];
int p[(int)1e7];
int main() {
  ios_base::sync_with_stdio(0);
  gets(s);
  pref_func(s, p);
  int n = strlen(s);
  if (p[n - 1]) {
    int sv = p[n - 1];
    deque<int> v;
    while (sv > 0) {
      v.push_back(sv);
      sv = p[sv - 1];
    }
    while (v.size()) {
      int sv = v.front();
      v.pop_front();
      for (int i = 0; i < n - 1; ++i) {
        if (p[i] == sv) {
          for (int j = 0; j < p[i]; ++j) {
            cout << s[j];
          }
          cout << "\n";
          return 0;
        }
      }
    }
  }
  cout << "Just a legend\n";
  return 0;
}
