Calculate natural logarithm of 2

#include <iostream>

int main (void)
{
    /*
    Write a program that prompts the user to enter a number then compute the natural logarithm of 2,
    by adding up to n terms in the series where n is the number that the user entered.

    1 - 1/2 + 1/3 - 1/4 + 1/5 -... 1/n
    */

    double sum = 0;
    int n = 1000;
    for (int i=1; i <= n; i=i+2)
    {
        sum += 1.0/i - 1.0/(i+1);
    }
    std::cout << sum;
}