#include <bits/stdc++.h>
using namespace std;
void ASS(bool b) {
  if (!b) {
    ++*(int*)0;
  }
}
#pragma comment(linker, "/STACK:106777216")
const int N = 1 << 20;
struct chash {
  int a[N];
  int p[N];
  int hash(int pos, int k) const { return a[pos + k] - a[pos] * p[k]; }
  void Init(char* s, int n, int h) {
    a[0] = 0;
    p[0] = 1;
    for (int i = 0; i < (int)(n); i++) {
      a[i + 1] = a[i] * h + s[i] - 'a' + 1;
      p[i + 1] = p[i] * h;
    }
  }
};
chash h0, h1;
char s[N];
vector<int> toDel[N];
int main() {
  scanf("%s", s);
  int n = (int)strlen(s);
  int H1 = 2999 + rand();
  for (int i = 0; i < (int)(n); i++) H1 = H1 * 2999 + s[i] - 1;
  H1 = (H1 & ((1 << 30) - 1)) | 1;
  h0.Init(s, n, 3731);
  h1.Init(s, n, H1);
  set<int> st;
  int BestLen = 0;
  int BestPos = 0;
  for (int i = 0; i < (int)(n); i++) {
    if (i == n - 1 || i == 0) continue;
    for (int j = 0; j < (int)(toDel[i].size()); j++) st.erase(toDel[i][j]);
    int L = 0;
    int R = n - i;
    while (R - L > 1) {
      int m = (L + R) >> 1;
      if (h0.hash(i, m) == h0.hash(0, m) && h1.hash(i, m) == h1.hash(0, m))
        L = m;
      else
        R = m;
    }
    if (L > 0) {
      st.insert(i);
      toDel[i + L].push_back(i);
    }
    L = 0;
    R = i + 1;
    while (R - L > 1) {
      int m = (L + R) >> 1;
      if (h0.hash(i - m + 1, m) == h0.hash(n - m, m) &&
          h1.hash(i - m + 1, m) == h1.hash(n - m, m))
        L = m;
      else
        R = m;
    }
    set<int>::iterator it = st.lower_bound(i - L + 1);
    if (it != st.end()) {
      int Len = i - (*it) + 1;
      if (BestLen < Len) {
        BestLen = Len;
        BestPos = (*it);
      }
    }
  }
  if (BestLen == 0) {
    printf("Just a legend\n");
  } else {
    s[BestPos + BestLen] = 0;
    printf("%s\n", s + BestPos);
  }
  return 0;
}
