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

int main(){
    char s[101];
    scanf("%[^\\n]",str);
    int len = strlen(str);
    int seen[256] = {0};
   
    for (int i=0;i<len;i++){
        if (!isalnum(str[i]) && str[i] !=' '){
            printf("Invalid input\n");
            return 0;
        }
    }
    for (int i=0;i<len;i++){
    if (!seen[(unsigned char)str[i]]){
        
            printf("%c", str[i]);
            seen[(unsigned char)str[i]] = 1;
        }
    }
    printf("\n");
    return 0;
}