  import java.util.*;

  public class Main {
      public static void main (String[]args){

          Scanner scanner = new Scanner(System.in);

          // 入力回数の取得
          int N = scanner.nextInt();

          double all = 0;

          for (int i = 0; N > i ; i++) {
            //　入力回数分の数値入力を求め、逆数に変換する
            all +=  1 / scanner.nextDouble();
          }

          // 逆数として出力
          System.out.println(1 / all);
              
      }
  } 
/tmp/hf-datasets-cache/medium/datasets/42704881117311-config-parquet-and-info-qiankunmu-Project_CodeNet-896c9d36/hub/datasets--qiankunmu--Project_CodeNet_Python800_and_Java250/snapshots/c899fde44a77ba1cc14973ed3de064e4ff3aadc7/Project_CodeNet_Java250.tar.gz