#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;
}