#include<stdio.h>

int main(void){
  
  int a , b ,n;
  scanf("%d %d %d",&a,&b,&n);
  int max = 0;
  
  
  for(int i = 0;i <= n;i ++){
    int floor = (a*i)/b - (a*(i/b));
    if(max<floor){
      max = floor;
    }
  }
  printf("%d",max);
  
  return 0;
}
