#include<stdio.h>
#include<string.h>
#include<ctype.h>

int main(){
    char s[101];
    char result[101] = "";
    int seen[256] = {0};
    
    fgets(s, sizeof(s), stdin);
    
    size_t len = strlen(s);
    if (s[len-1] == '\n') s[len-1] = '\0';
    
    for (int i=0;s[i] != '\0';i++){
        if (!isalpha(s[i]) && !isdigit(s[i]) && s[i] !=' '){
            
            printf("Invalid input\n");
            return 0;
            
        }
        
    }
    for(int i=0;s[i] != '\0'; i++){
        if 
        
        
        
        
        
        

        if (!seen[(unsigned char)s[i]]){
            strncat(result, &s[i], 1);
            seen[(unsigned char)s[i]] = 1;
        }
    }
    printf("%s\n", result);
    return 0;
}