import java.util.Scanner;

import java.text.DecimalFormat;


public class Main {

        public static void sequence(int N){

                DecimalFormat df = new DecimalFormat("0.00");

                float sum = 0;

                float A1 = 2;

                float A2 = 3;

                float B1 = 1;

                float B2 = 2;

                if(N>=1){

                        sum = A1/B1;

                        if(N>=2){

                                sum += A2/B2;

                                if(N>=3){

                                        for(int i=2;i<N;i++){

                                                float A3 = A2+A1;

                                                float B3 = B2+B1;

                                                sum+=A3/B3;

                                                A1=A2;

                                                A2=A3;

                                                B1=B2;

                                                B2=B3;

                                        }

                                }

                        }

            System.out.print(df.format(sum));

                }

        }

        public static void main(String[] arg){

                Scanner sc = new Scanner(System.in);

                int N = sc.nextInt();

                sequence(N);

        }

}


 

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