#include <assert.h>
#include <err.h>
#include <stdio.h>

char nybble(int n) {
	assert(0 <= n && n <= 15);
	return "0123456789abcdef"[n];
}

int main(void) {
	for (;;) {
		int byte = getchar();
		if (byte == EOF) {
			if (feof(stdin)) {
				break;
			} else {
				err(1, "Error reading byte");
			}
		}

		if (putchar(nybble(byte >> 4)) == EOF) {
			err(1, "Error writing high nybble");
		}
		if (putchar(nybble(byte & 0xf)) == EOF) {
			err(1, "Error writing low nybble");
		}
	}

	if (putchar('\n') == EOF) {
		err(1, "Error writing terminating newline");
	}

	if (fflush(stdout) == EOF) {
		err(1, "Error flushing stdout");
	}

	return 0;
}