ex88 pg63

#include<iostream>
#include<iomanip>
#include<cmath>
using namespace std;
int main()
{
        int n,i;
        double s=0;
        cin>>n;
        for(i=1;i<=n;i++)
        {
            if(i%2) s=s+sqrt(i);
            else
                s=s-sqrt(i);
        }
        cout<<setprecision(4)<<fixed<<floor(s*10000)/10000;
}