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