#include <bits/stdc++.h>
using namespace std;
int z_algo(char* s, int** zz);
int main() {
  int TC = 1;
  int* z;
  while (TC--) {
    char a[1000001];
    char g[1000001 * 2];
    strcpy(a, "");
    strcpy(g, "");
    scanf("%s", a);
    strcat(g, a);
    strcat(g, "$");
    strcat(g, a);
    z_algo(g, &z);
    int lenG = strlen(g);
    int lenA = strlen(a);
    int i = 0;
    int res = 0;
    for (i = lenA + 2; i < lenG; i++) {
      if (z[i] > 0) {
        if (z[res] < z[i]) {
          res = i;
        }
      }
    }
    if (z[res] > 0) {
      for (i = res + 1; i < lenG; i++) {
        if (z[i] <= z[res] && i + z[i] == lenG) {
          printf("%s\n", g + i);
          break;
        }
      }
    }
    if (i == lenG) {
      printf("Just a legend\n");
    }
  }
  return 0;
}
int z_algo(char* s, int** zz) {
  int result = 0;
  int len = strlen(s);
  result = len;
  int* z = (int*)calloc(len, sizeof(int));
  *zz = z;
  int r = 0, l = 0, i = 0, j = 0, _k = 0, _b = 0;
  for (int k = 1; k < len; k++) {
    if (k > r) {
      i = 0;
      j = k;
      while (j < len && s[i] == s[j]) {
        i++;
        j++;
      }
      if (j - k > 0) {
        l = k;
        r = j - 1;
        z[k] = j - k;
      }
    } else {
      _k = k - l;
      _b = r - k + 1;
      if (z[_k] < _b) {
        z[k] = z[_k];
      } else {
        i = _b;
        j = r + 1;
        while (j < len && s[i] == s[j]) {
          i++;
          j++;
        }
        if (j >= r + 1) {
          l = k;
          r = j - 1;
          z[k] = j - k;
        }
      }
    }
    result += z[k];
  }
  return result;
}
