#include <stdio.h>
#include <limits.h>
#include <string.h>
#include <ctype.h>         

int main() {
        FILE *stream;
        char buffer[LINE_MAX];
        int run;

        int empty(char*);
        if ((stream = fopen("channel", "r+"))) run = 1;
        else
        {
                run = 0;
                perror("!.!..blad otwarcia lacza..!.!");
        }

        while (run) {
                bzero((void*)buffer,LINE_MAX);
                fgets(buffer,LINE_MAX,stdin);
                if (!empty(buffer))
                {
                        fprintf(stream, "%s\n", buffer);
                        fflush(stream);
                }
                else {
                        fclose(stream);
                        break;
                }
                fgets(buffer,LINE_MAX,stream);
                if (!empty(buffer))
                {
                       fprintf(stdout, "%s\n",buffer );
                       fflush(stream);
                }

        }
        return 0;
}

int empty(char * string) {
        while (*string) {
                if (isalnum(*string++))
                {
                        return 0;
                }
        }
        return 1;
}