#include<stdio.h>

int floor(long long a, long long b){
  int c = a/b;
  return(c);
}

int main()
{
  long long a,b,n;
  scanf("%lld %lld %lld",&a,&b,&n);
  long long max = 0;
  long long temp = 0;
  int count =0;
  int max_count = 0;

  for(int i=1; i<=n; i++){
    temp = floor(a*i,b) - a*floor(i,b);
    count ++;
    temp = temp / 1;
    if(temp > max){
      max = temp;
      max_count = max;
    }
  }

  printf("%lld",max);

}

