z10

#include <iostream>

int main()
{
    double x, suma(0), b;
    int n;
        std::cout<<"Unesi jedan realan i prirodan broj: ";
    std::cin>>x>>n;
    for (int k=1; k<=n; k++)
    {  suma+=x*(x+k);

        if (k%2==0)
             b=1/suma;
        else b*=(-1);
    }
    std::cout<<b;
    return 0; }