// editor5
#include<stdio.h>
#include<string.h>
#include<ctype.h>
int main(){
    char s[101];
    int count[256] = {0};
    fgets (s,sizeof(s),stdin);
    s[strcspn(s,"\n")] = '\0';
    for(int i=0;s[i] != '\0'; i++){
        if(!isalnum(s[i] || s[i] == '')){
            printf("Invalid input");
            return 0;
        }
        if(s[i] != ' '){
            count[(unsigned char)s[i]]++;
        }
    }
    for(int i=0;s[i] != '\0';i++){
        if(s[i] != ' ' && count[(unsigned char)s[i]] == 1){
            printf("%c",s[i]);
        }
    }
    return 0;
}