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

int main() {
    char str[105];
    if(fgets(str, sizeof(str),stdin) ==NULL){
        printf("Invalid input");
        return 0;
    }
    
    int len = strlen(str);
    if(str[len - 1] == '\n') str[len - 1]='\0';
    for(int i = 0; str[i]!='\0';i++){
        if(!isalnum(str[i]&&str[i]!=''))
        printf("Invalid input");
        retirn 0;
        }
    }
 int seen[256]={0};
 for(int i =0; str[i]!='\0';i++) {
    if(!seen[(unsigned char)str[i]]){
        printf("%c", str[i]);
        seen[(unsigned char)str[i]]= 1;
    }
}
return 0;
}