#include <bits/stdc++.h>
using namespace std;
bool check(long long n, long long pos) { return n & (1LL << pos); }
long long Set(long long n, long long pos) { return n = n | (1LL << pos); }
long long basei[1000006];
long long hasht[1000006];
char str[1000006];
vector<long long> ps;
long long mul(long long a, long long b) {
  return ((a % 999998683) * (b % 999998683)) % 999998683;
}
long long hsh(long long l, long long r) {
  return (hasht[r] - hasht[l - 1] + 999998683) % 999998683;
}
bool solve(long long len, long long n) {
  long long bhash = hsh(1, len);
  for (long long i = 2; i + len - 1 < n; i++) {
    long long chash = hsh(i, i + len - 1);
    if (mul(bhash, basei[i - 1]) == chash) return 1;
  }
  return 0;
}
long long bs(long long n) {
  long long lo = 0;
  long long hi = ps.size() - 1;
  long long ret = -1;
  while (lo <= hi) {
    long long mid = (lo + hi) / 2;
    if (solve(ps[mid], n)) {
      ret = mid;
      lo = mid + 1;
    } else {
      hi = mid - 1;
    }
  }
  return ret;
}
int main() {
  long long i, j, k, l, m, n, o, r, q;
  long long testcase;
  long long input, flag, tag, ans;
  basei[0] = 1;
  for (i = 1; i <= 1000000; i++) {
    basei[i] = mul(basei[i - 1], 3323);
  }
  while (scanf("%s", str + 1) != EOF) {
    n = strlen(str + 1);
    for (i = 1; i <= n; i++) {
      hasht[i] = mul(str[i], basei[i]);
      hasht[i] = (hasht[i] + hasht[i - 1]) % 999998683;
    }
    ps.clear();
    for (i = 1; i < n; i++) {
      if (mul(hsh(1, i), basei[n - i]) == hsh(n - i + 1, n)) {
        ps.push_back(i);
      }
    }
    ans = bs(n);
    if (ans == -1)
      printf("Just a legend\n");
    else {
      ans = ps[ans];
      for (i = 1; i <= ans; i++) printf("%c", str[i]);
      printf("\n");
    }
  }
}
