#include<stdio.h>
#include<string.h>
#include<ctype.h>
int main(){
    charvstr[101],result[101];
    int seen[256] = {0};
    int i,j = 0,invalid = 0;
    fgets(str, sizeof(str), stdin);
    str[strcspn(str, "\n")]='\0';
    for(i=0;str[i] != '\0'; i++){
        if(!(isalnum(str[i]) || str[i] == ' ')){
            invalid=1;
            break;
        }
    }
    if(invalid){
        printf("Invalid input\n");
        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\n",result);
    return 0;
}