#include<stdio.h>
#include<string.h>
#include<ctype.h>
int main(){
    char s[101];
    int visited[256] = {0};
    fgets(s, sizeof(s),stdin);
    s[strcspn(s, "\n")] = '\0';
    for(int i = 0; s[i] != '\0'; i++){
        if(!(isalnum(s[i]) || s[i] == '')){
            printf("Invalid input");
            return 0;
        }
    }
    for(int i = 0; s[i] !='\0';i++){
        if(!visited[(unsigned char)s[i]]){
            printf("%c",s[i]);
            visited[(unsigned char)s[i]]=1;
        }
    }
    return 0;
}