ar@cello ~ % gcc -o crayon crayon.c
ar@cello ~ % cat crayon.c
#include <stdio.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/wait.h>

int
main(int argc, char **argv)
{
    int k, can = 0;
    int status = 0;
    pid_t pid;
    while (fscanf(stdin, "%d", &k) != EOF)
    {
        pid = fork();
        if(pid < 0)
        {
            fprintf(stdout, "-1\n");
            return can ? 35 : 0;
        }
        if(pid > 0)
        {
            fclose(stdin);
            wait(&status);
            if((WIFEXITED(status) && WEXITSTATUS(status) == 35) || WIFSIGNALED(status))
            {
                return can ? 35 : 0;
            }
            printf("%d\n", k);
            return 0;
        }
        can += 1;
    }
    return 0;
}
ar@cello ~ % seq 1 20 | bash -c 'ulimit -u 20; exec ./crayon'
-1
ar@cello ~ % seq 1 30 | bash -c 'ulimit -u 20; exec ./crayon'
-1
ar@cello ~ % seq 1 34 | ./crayon | wc -l                 
34
ar@cello ~ %