#include <stdio.h>
#include <stdlib.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>

#define DEFSIZE 10
#define MAXSIZE 70

int main (int argc, char **argv)
{
    int file, digits = -1, i; long unsigned int value; size_t size;
    
    // Se abre /dev/random
    file = open("/dev/random", O_RDONLY);
    if (file == -1) {perror("open"); exit(EXIT_FAILURE);}
    
    // Se obtiene el número de fígitos
    if (argc > 1) digits = atoi(argv[1]);
    if (digits <= 0) digits = DEFSIZE;
    if (digits > MAXSIZE) digits = MAXSIZE;
    
    // Se obtienen e imprimen los valores aleatorios desde random
    size = sizeof(value);
    do {            
        if (read(file, &value, size) == -1)
            {perror("read"); exit(EXIT_FAILURE);}
        if (digits > 5)
            {value=value%100000; digits=digits-5; printf("%05lu",value);}
        else
            {value=value%10; digits=digits-1; printf("%1lu",value);}
    } while (digits > 0);
        
    putchar('\n'); exit(EXIT_SUCCESS); // Y fin
}