#include<stdio.h>

int main(void)
{
	unsigned long long int a, b, c;
	unsigned long long int max;
	

	scanf("%lld%lld%lld", &a, &b, &c);

	if (c >= b) {
		max = (unsigned long long int)(a * (b - 1) / b);
	}

	else {
		max = (unsigned long long int)(a * c / b);
	}

	printf("%lld", max);

	return 0;
}