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