#include <bits/stdc++.h>
using namespace std;
const int M = 101, N = 1000000;
const long long MOD1 = 1e9 + 7, MOD2 = 1e9 + 9;
long long h1[N], h2[N], p1[N], p2[N];
string s;
int n, tobs[N], cnt;
int get1(int i, int len) {
  return (((h1[i + len - 1] - (i ? h1[i - 1] : 0) * p1[len]) % MOD1) + MOD1) %
         MOD1;
}
int get2(int i, int len) {
  return (((h2[i + len - 1] - (i ? h2[i - 1] : 0) * p2[len]) % MOD2) + MOD2) %
         MOD2;
}
bool ok(int idx) {
  int len = tobs[idx];
  pair<int, int> val = {get1(0, len), get2(0, len)};
  if (val != make_pair(get1(n - len, len), get2(n - len, len))) return 0;
  for (int i = 1; i < n - 1; ++i) {
    if (i + len >= n) break;
    if (make_pair(get1(i, len), get2(i, len)) == val) return 1;
  }
  return 0;
}
int f(int lo, int hi) {
  if (lo == hi) {
    return lo;
  }
  int mid = (lo + hi) / 2 + 1;
  if (ok(mid)) {
    return f(mid, hi);
  } else {
    return f(lo, mid - 1);
  }
}
int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  cin >> s;
  n = s.length();
  p1[0] = p2[0] = 1;
  for (int i = 1; i < n; ++i) {
    p1[i] = p1[i - 1] * M;
    p2[i] = p2[i - 1] * M;
    p1[i] %= MOD1, p2[i] %= MOD2;
  }
  for (int i = 0; i < n; ++i) {
    h1[i] = (i ? h1[i - 1] : 0) * M + s[i];
    h2[i] = (i ? h2[i - 1] : 0) * M + s[i];
    h1[i] %= MOD1, h2[i] %= MOD2;
  }
  tobs[0] = 0;
  cnt = 1;
  for (int i = 1; i < n; ++i) {
    if (make_pair(get1(0, i), get2(0, i)) ==
        make_pair(get1(n - i, i), get2(n - i, i))) {
      tobs[cnt++] = i;
    }
  }
  int ans = 0;
  if (cnt) {
    ans = f(0, cnt - 1);
  }
  if (ans == 0) {
    cout << "Just a legend\n";
  } else {
    cout << s.substr(0, tobs[ans]) << "\n";
  }
}
