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

int main()
{
	double B,N,C;
	int A,max = 0;

	scanf("%d %lf %lf",&A,&B,&N);

	for (double x = 0;x <= N;x++){
		C = floor(A * x / B) - A * floor(x / B);
		if (max < C) max = C;
	}

	printf("%d\n",max);

	return 0;
}
