#include<stdio.h>
#include<string.h>
#include<ctype.h>
int main(){
    char s[200];
    int freq[256]={0};
    if(!fgets(s,sizeof(s),stdin)) return 0;
    s[strcspn(s,"\n")]='\0';
    for(int i=0;s[i]!='\0';i++)
}
     
    unsigned char c=(unsigned char)s[i];
      if(!(isalnum(c)||c==' ')) {
          printf("Invalid input");
          return 0;
      }
      freq[c]++;
      }
      char out[250];
      int j=0;
      for(int i=0;s[i]!='\0';++i){
          unsigned char c=(unsigned char)s[i];
          if(freq[c]==1)out[j++]=s[i];
      }
      out[j]='\0';
      printf("%s",out);
      return 0;
      }