#include<stdio.h>

long long my_floor(double);

int main(){
  double A,B,N;
  long long x,ans;

  scanf("%lf %lf %lf",&A,&B,&N);

  ans = -1;
  for(x = 1;x <= N;x++){
    if(my_floor(A * x / B) - A * my_floor(x / B) > ans){
      ans = my_floor(A * x / B) - A * my_floor(x / B);
    }else{
      break;
    }
  }

  printf("%lld\n",ans);

  return 0;
}

long long my_floor(double x){
  return (long long)x;
}
