#include<stdio.h>

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

    