#include <stdio.h>
#include <stdlib.h>

int main (int N)
{
  int c;
  N = 3;
  int i = 0;
  int MAX;

  char *pole = malloc(100*sizeof(char));
  if(pole == NULL)
    return 0;

  while((c=getchar()) != EOF)  {
    pole[i] = (char)c;
    i++;
  }

  MAX = i;
  i = 0;

  for(int k = 0; k < 3; k++)
  {

    if((i + N) < MAX && pole[i] == pole[i+N])
      {
      putchar(pole[i]);
      i++;
      }
  }


  free(pole);
  return 1;

}