#include <stdio.h>

int main(void) {
	int max = 0, pt, n1, n2, a_i;
	double num1, num2, a, b, n;
	scanf("%lf%lf%lf", &a, &b, &n);

	a_i = a;

	for (double i = 0; i <= n; i++) {
		num1 = (a * i / b);
		num2 = (i / b);
		n1 = num1;
		n2 = num2;
		pt = n1 - a * n2;
		if (i == 0 || max < pt)
			max = pt;
	}

	printf("%d", max);

	return 0;
}