#include<stdio.h>
#include<math.h>

int main()
{
	double A;
	double B;
	long long N;
	double maxval=0;
	double val;

	scanf("%lf %lf %lld",&A,&B,&N);
	for(long long i = 0; i<=N;i++)
	{
		val = floor(i*A/B) - A*floor(i/B);
		if (val>maxval) maxval=val;
	}
	printf("%lld\n",(long long)maxval);

	return 0;
}
