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