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