import 'dart:io';

void main(){
  List<String> inputStrList = stdin.readLineSync().split(' ');
  int a = int.parse(inputStrList[0]);
  int b = int.parse(inputStrList[1]);
  int n = int.parse(inputStrList[2]);

  if(b <= n){
    print((a * (b - 1) / b).floor() - a * ((b - 1) / b).floor());
  }else{
    print((a * n / b).floor() - a * (n / b).floor());
  }
}