#include<stdio.h>
int main()
{
	unsigned long a,b,n;
	scanf("%lu %lu %lu",&a,&b,&n);
	unsigned long i,max=0;
    unsigned long tmp1,tmp2;
	for(i=1;i<n+1;i++){
      tmp1=a*i/b;
      tmp2=i/b;
      if(tmp1-a*tmp2>max){
        max=tmp1-a*tmp2;
      }
	}
  printf("%lu",max);
	return 0;
}