#include <stdio.h>

int main(void) {
	long long int max = 0, pt, a, b, n;
	scanf("%lld%lld%lld", &a, &b, &n);

	for (int i = 0; i <= n; i++) {
		pt = ((a * i) / b) - (a * (i / b));
		if (i == 0 || max < pt)
			max = pt;
	}

	printf("%lld", max);

	return 0;
}