#include<stdio.h>
#include<string.h>
#include<ctype.h>
int main(){
    char s[1000],ch;
    int freq[256]={0};
    int i,j=0;
    
    if(fgets(s,sizeof(s),stdin)==NULL){
        printf("Invalid input");
        return 0;
    }
    size_t len=strlen(s);
    if(len>0 && s[len-1]=='\n')
    s[len-1]='\0';
    
    for(i=0;s[i];i++){
        unsigned char ch=s[i];
        if(!(isalpha(ch) || ch==' ')) {
            printf("Invalid input");
            return 0;
        }
        if(ch!=' ')
        freq[tolower(ch)]++;
    }
        char result[1000];
        unsigned char lowerCh=tolower(ch);
        if(ch!=' ' && freq[lowerCh]==1){
            result[j++]=islower(ch) ? toupper(ch):ch;
        }
    }
    
    result[j]='\0';
    
    printf("%s\n",result);
    return 0;
}