#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;
}