#include<stdio.h>
#include<string.h>
#include<ctype>
int main(){
    char s[201];
    if(!fgets(s, sizeof s,stdin)) return 0;
    int n= strlen(s);
    if(n>0 && s[n-1] == '\n'){ s[n-1] ='\0';
n--;    
}
int freq[256] ={0};
for (int i=0;i<n; ++i){
    unsigned char c=(unsigned char)s[i];
    if(!(isalnum(c) || c==' ')){
        printf("Invalid input");
        return 0;
    }
    freq[c]++;
}
for(int i=0;i<n; ++i){
    unsigned char c=(unsigned char)s[i];
    if(freq[c == 1]) putchar(c);
}
return 0;
}