#include<stdio.h>

int main(void) {
	
	int a, b, n, x, max=-100000, tmp;

	scanf("%d %d %d", &a, &b, &n);

	for (x = 0; x <= n; x++) {
		tmp = (int)(a*x / b) - a * (int)(x / b);
		if (tmp > max) max = tmp;
	}

	printf("%d", max);

	return 0;
}