#include<stdio.h>
#include<ctype.h>
#include<string.h>
int main(void)
{
    char s[1001];
    if(!fgets(s,sizeof(s),stdin))
    return 0;
    size_t len=strlen(s);
    if(len &&s[len-1]=='\n')s[--len]='\0';
    for(size_t i= 0;i < len;i++)
    {
        if(!(isalnum((unsigned char)s[i])||s[i]==' '))
        
        {
            printf("Invalid input");
            return 0;
        }
    }
    int seen[256]={0};
    char out[1001];
    size_t k=0;
    for(size_t i=0;i<len;i++)
    {
        unsigned char c=(unsigned char )s[i];
        if(!seen[c])
        {
            seen[c]=1;
            out[k++]=(char)c;
        }
    }
    out[k]='\0';
    printf("%s",out);
    return 0;
}
        }
    }
            
        }'))
    }
    '
}