#include <bits/stdc++.h>
#pragma warning(disable : 4786)
#pragma comment(linker, "/STACK:16777216")
using namespace std;
char str[1000005];
int Z[1000005], n;
void Zfunction() {
  int L, R, r, i, j, k;
  L = 0;
  R = 0;
  Z[0] = 0;
  for (i = 1; i < n; i++) {
    if (i > R) {
      L = i;
      R = i;
      while (R < n && str[R - L] == str[R]) R++;
      Z[i] = R - L;
      R--;
    } else {
      r = i - L;
      if (Z[r] < R - i + 1)
        Z[i] = Z[r];
      else {
        L = i;
        while (R < n && str[R - L] == str[R]) R++;
        Z[i] = R - L;
        R--;
      }
    }
  }
}
int max(int a, int b) {
  if (a > b) return a;
  return b;
}
int main() {
  int i, j, k, maxr, res;
  while (scanf("%s", str) != EOF) {
    n = strlen(str);
    maxr = 0;
    res = 0;
    Zfunction();
    for (i = 0; i < n; i++) {
      if (Z[i] == n - i) {
        if (maxr >= n - i) {
          res = n - i;
          break;
        }
      }
      maxr = max(maxr, Z[i]);
    }
    if (res == 0 || n <= 2)
      printf("Just a legend\n");
    else {
      for (i = 0; i < res; i++) printf("%c", str[i]);
      printf("\n");
    }
  }
  return 0;
}
