#include<stdio.h>
#include<math.h>
int main(void){
	int x,A,B,N;
	double a,b,n,s,t,F,max;
	scanf("%d %d %d",&A,&B,&N);
	a=1.0*A;
	b=1.0*B;
	n=1.0*N;
	max=0;
	for(x=0;x<=n;x++){
		s=1.0*a*x/b;
		t=1.0*x/b;
		F=floor(s)-a*floor(t);
		if(max<F){
			max=F;
		}
	}
	printf("%d\n",floor(max));
	return 0;
}

	
		