#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;
  
      if(a<b)
      {
     c=(a*d)/b;
     e=d/b;
     f=a*f;
     if(max<(c-f)) max=c-f;
      }
      
      else{
         while(d<n)
         {
         d=d+b;
         }
        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;
}