#include<stdio.h>
int main()
{
long long int a,b,n,i,max,c,d,e,f;
  max=0;
  scanf("%lld %lld %lld",&a,&b,&n);

  if(a==b || b>n) 
  {c=a*n/b;
   e=n/b; 
   f=a*e;
   printf("%lld",c-f);}
  
  
 else{ d=b-1;
  while(d<n)
     {
     c=(a*d)/b;
     e=d/b;
     f=a*f;
     if(max<(c-f)) max=c-f;
     d=d+b;
     }
   c=a*n/b;
   e=n/b; 
   f=a*e;
   if(max>(c-f))  max=c-f;
    printf("%lld",max);}
  
return 0;
}