#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 = strlren(s);
if(len>0&&s[len-1]=='\n'){
s[len-1]='\0';
len--;
}
if(len==0){
putchar('\n');
return 0;
}
int freq[256]={0};
for (size_t i=0;i<len;++i){
unsigned char c = (unsigned char)s[i];
if (!(isalnum(c)||c=='')) {
printf("invalid input\n");
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;
}