>>100
#include <stdio.h>
#include <string.h>

int center_char_of_string(const char * str, int length)
{
  return str[(length - 1) / 2];
}

int main(void)
{
  char buf[256], dest[256] = {'\0'};
  int  i;
  for (i = 0; i < sizeof(dest) - 1 && scanf("%255s", buf) == 1; i++) {
    dest[i] = center_char_of_string(buf, strlen(buf));
  }

  puts(dest);

  return 0;
}