#include<stdio.h>
#include<math.h>
#include<string.h>
#include<stdlib.h>
#include<math.h>
long long int floor_(float x){
 return (long long int)x/1;}

int main(){
 long long a,b,n;
 scanf("%lld%lld%lld",&a,&b,&n);
 
 if(n<b){
  printf("%lld\n",floor_(a*(float)n/(float)b));
  return 0;}
 
 if(n==b){
  printf("%lld\n",floor_(a*(float)(n-1)/(float)b));
  return 0;}
  
 else{
   printf("lld\n",floor_(a*(float)(n/b*b-1)/(float)b));
  return 0;}

} 