#include <u.h>
#include <ctype.h>
#include <libc.h>
#include <bio.h>

Biobuf bin, bout;

int main()
{
	long got;
	char buf[1024], *p;

	Binit(&bin, 0, OREAD);
	Binit(&bout, 1, OWRITE);

	while((got = Bread(&bin, buf, sizeof(buf))) > 0){
		for (p = buf; p < buf + got; p++)
			if (isalpha(*p))
				if (tolower(*p) <= 'm')
					*p += 13;
				else
					*p -= 13;
		Bwrite(&bout, buf, got);
	}
	Bterm(&bout);
}