#include<stdio.h>
#include<string.h>
#include<ctype.h>
int main(){
    char s[101];
    char result[101];
    int freq[256]={0};
    int result_idx = 0;
    int has_special_char = 0;
    fgets(s,sizeof(s),stdin);
    s[strcspn(s,"\n")] = 0;
    for(int i=0;i<strlen(s);i++){
        char c=s[i];
        if(!isalnum(c)&& !isspace(c)){
            has_special_char=1;
            break;
        }
        if(freq[(unsigned)c]==0){
            result[result_idx++]=c;
            freq[(unsigned char)c]=1;
        }
    }
    if(has_special_char){
        printf("Invalid input\n");
    }else{
        result[result_idx]='\0',
        pintf("%s\n",result);
    }
    return 0;
}