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

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

  
return 0;
}