#include<stdio.h>
#include<string.h>
#include<ctype.h>
int main(void){
  char s[256];
  if(!fgets(s,sizeof(s),stdin))return 0;
  size_t len=strlen(s);
  if(len>0&&s[len-1]=='\n'){
    s[len-1]='\0';
    len--;
}
if (len==0){
  putchar('\n');
  return 0;
 }
 int freq[100]={0};
 for(size_t i=0;i<len;i++){
   unsigned char c=(unsigned char)s[i];
   if(!(isalnum(c)||c==' ')){
   printf("Invalid input");
   return 0;
   }
   freq[c]++;
 }
for(size_t i=0;i<len;i++){
   unsigned char c=(unsigned char)s[i];
   if(freq[c]==1)putchar(c);
}
putchar('\n');
return 0;