#include<stdio.h>
#include<math.h>
int main()
{
    double a,b,n,i,x;

    while(scanf("%lf %lf %lf",&a,&b,&n)!=EOF)
    {
        double max = 0;

        for(x=1;x<=n;x++)
        {
            i = (floor)((a*x)/b) - (a*(floor)(x/b));
            if(i>max)
            {
                max = i;
            }
        }

        printf("%.0lf\n",max);
    }

    return 0;
}
