int main(void)
{
    int a, b, n;
    int x, f;
    int ans = -100;
    int axb, xb;
    scanf("%d%d%d",&a,&b,&n);
    
    for(x=1;x<=n;x++){
        axb = (a*x)/b;
        xb = x/b;

        f = axb - a * xb;

        if(f>=ans){
            ans = f;
        }
    }
printf("%d\n",ans);

return 0;
}