#include<stdio.h>
#include<string.h>
#include<ctype.h>
int main(){
    char str[1000], result[1000];
    int seen[256]={0};
    int i,j=0;
    fgets(str,sizeof(str),stdin);
    str[strcspn(str, "\n")]='\0';
    for(i=0;str[i]!='\0';i++){
        if(!(isalnum(str[i]) || issapce(str[i]))){
            printf("Invalid ");
            return 0;
        }
    }
    for(i=0;str[i]!='\0';i++){
        if(!seen[(unsigned char)str[i]]){
            result[j++]=str[i];
            seen[(unsigned char)str[i]]=1;
        }
    }
    result[j]='\0';
    printf("%s",result);
    return 0;
}