#include<stdio.h>
 main()
 {
     double i,sum=0;
     int k=3,m;
     scanf("%d",&m);
     for(i=1.0;k<m+3;k++,i++)
         {  
            for(;k%2==0;)
             sum-=1/i;
           for(;k%2==1;)
            sum+=1/i;                      
......................