#include <bits/stdc++.h>
using namespace std;
const int N = 1000500;
const int INF = 1000000000, mod = 1000000007;
const long long LLINF = 1000000000000000000ll;
char s[N];
int z[N];
int cnt[N];
int n;
void calcZ() {
  int l = 0, r = 0;
  for (int i = 1; i < n; ++i) {
    if (i <= r) {
      z[i] = min(z[i - l], r - i + 1);
    }
    while (i + z[i] < n && s[z[i]] == s[i + z[i]]) {
      z[i]++;
    }
    if (i + z[i] >= r) {
      l = i;
      r = i + z[i] - 1;
    }
    cnt[z[i]]++;
  }
}
int main() {
  scanf("%s", &s);
  n = strlen(s);
  calcZ();
  int cur = 0;
  for (int i = n; i >= 1; --i) {
    cur += cnt[i];
    if (cur >= 2 && z[n - i] == i) {
      for (int j = 0; j < i; ++j) {
        putchar(s[j]);
      }
      exit(0);
    }
  }
  puts("Just a legend");
  return 0;
}
