#include <stdio.h>

int
lower(int c)
{
	if (c >= 'A' && c <= 'Z') {
		return c + 'a' - 'A';
	} else {
		return c;
	}
}

int
atoi(char s[])
{
	int i, n;

	n = 0;
	for (i = 0; s[i] >= '0' && s[i] <= '9'; ++i) {
		n = 10 * n + (s[i] - '0');
	}
	return n;
}

/* convert string of hex digits into int digits */
int
htoi(char s[])
{
	int i, n;

	n = 0;
	for (i = 0; s[i] >= '0' && s[i] <= 'f'; ++i) {
		if (s[i] >= '0' && s[i] <= '9') {
			n = 16 * n + (s[i] - '0');
		} else if (s[i] >= 'A' && s[i] <= 'F') {
			n = 16 * n + (s[i] - 'A' + 10);
		} else if (s[i] >= 'a' && s[i] <= 'f') {
			n = 16 * n + (s[i] - 'a' + 10);
		}
	}
	return n;
}

int
main()
{
	printf("%d\n", htoi("1f"));
	return 0;
}