#include <bits/stdc++.h>
using namespace std;
using ll = long long;
ll md = 1000000007;
ll exp(ll a, ll b) {
  ll r = 1ll;
  while (b > 0) {
    if (b & 1) {
      r = r * (a % md);
      r = (r + md) % md;
    }
    b >>= 1;
    a = (a % md) * (a % md);
    a = (a + md) % md;
  }
  return (r + md) % md;
}
ll gcd(ll a, ll b) {
  if (b == 0) return a;
  return gcd(b, a % b);
}
ll Min(ll a, ll b) {
  if (a < b) return a;
  return b;
}
ll Max(ll a, ll b) {
  if (a > b) return a;
  return b;
}
long long n;
string s;
int32_t main() {
  ios::sync_with_stdio(false);
  cin.tie(NULL);
  cout.tie(NULL);
  cin >> s;
  n = s.size();
  long long ppow[n], phash[n + 5];
  long long p = 31, md = 1e9 + 9;
  ppow[0] = 1;
  phash[0] = 0;
  for (ll i = 1; i <= n - 1; ++i) ppow[i] = (ppow[i - 1] * p) % md;
  for (ll i = 0; i <= n - 1; ++i)
    phash[i + 1] = (phash[i] + (s[i] - 'a' + 1) * ppow[i]) % md;
  for (long long i = n - 2; i >= 1; --i) {
    long long x = phash[i], y = (phash[n] - phash[n - i] + md) % md, temp = x;
    x = (x * ppow[n - i]) % md;
    if (x == y) {
      for (ll j = 1; j <= n; ++j) {
        if (j + i >= n) break;
        long long z = (phash[j + i] - phash[j] + md) % md;
        long long w = (temp * ppow[j]) % md;
        if (w == z) {
          for (ll k = 0; k <= i - 1; ++k) cout << s[k];
          return 0;
        }
      }
    }
  }
  cout << "Just a legend";
  cout << '\n';
  return 0;
}
