#include<stdio.h>
#include<string.h>
#include<ctype.h>
int main(){
    char str[101];
    scanf("%100[^\n]",str);
    int seen[256]={0};
    char result[101];
    int idx=0;
    for(int i=0;str[i]!='\0';i++){
    char ch = str[i];
    if(!isalnum(ch)&&ch!=''){
        printf("Invalid input");
        return 0;
    }
    if(!seen[(unsigned char)ch]){
        result[idx++]=ch;
        seen[(unsigned char)ch]=1;
    }
}
result[idx]='\0';
printf("%s",result);
return 0;
}