#include<stdio.h>
int main()
{
	unsigned long long a, b, n,x;
	scanf("%lld%lld%lld", &a, &b, &n);
	if (n < b - 1) printf("%lld", (a*n)/b-a * (n / b));
	else
	{
		x = b - 1;
		printf("%lld", (a * x) / b - a * (x / b));
	}
	return 0;
}