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