#include<stdio.h>
#include<string.h>
#include<ctype.h>
int main(){
    char s[105];
    if(!fgets(s,sizeof(s),stdin)){
        printf("Invalid input\n");
        return 0;
    }
    s[strcs(s,"\n")]'\0';
    int len=strlen(s);
    for(int i=0;i<len;i++){
        if(!(isalnum(s[i]) || s[i] =='')) {
            printf("Invalid input");
            return 0;
        }
    }
    int seen[256]={0};
    int k=0;
    for(int i=0;i<len;i++){
        if(s[i]==' ')
        continue;
    unsigned char lower= tolower(s[i]);
    if(!seen[lower]){
        seen[lower]=1;
        result[k++]=s[i];
    }
        
    }
    result[k] ='\0';
    printf("%s\n",result);
    return 0;
}