Чему равна сумма 10^10 членов гармонического ряда?

#include <iostream>
 
int main ()
{
    const long long STOP = 10000000000;
    long double sum = 0.0;
    for (long long k=1; k<=STOP; ++k)
        sum += (1.0 / k);
    std::cout << std::fixed;
    std::cout.precision(12);
    std::cout.setf(std::ios_base::showpoint);
    std::cout << "\nFinally, sum = " << sum << std::endl << std::endl;
    return 0;
}

#include <iostream>
 
int main ()
{
    const int STOP = 1;
    long double sum = 1.0 / 10000000000.0;
    for (long long k=9999999999; k<STOP; --k)
        sum += (1.0 / k);
    std::cout << std::fixed;
    std::cout.precision(12);
    std::cout.setf(std::ios_base::showpoint);
    std::cout << "\nFinally, sum = " << sum << std::endl << std::endl;
    return 0;
}

k<STOP

    wchar_t buf[500];
    char bufc[500];
    _gcvt(sum, 50, bufc);
    wsprintfW(buf, L"%S", bufc);
    SetWindowTextW(hwndSta3, buf);

#include <iostream>
 
int main ()
{
    const int STOP = 0;
    long double sum = 1.0 / 10000000000.0;
    for (long long k=9999999999; k>STOP; --k)
        sum += (1.0 / k);
    std::cout << std::fixed;
    std::cout.precision(12);
    std::cout.setf(std::ios_base::showpoint);
    std::cout << "\nFinally, sum = " << sum << std::endl << std::endl;
    return 0;
}

    unsigned long long  N = 10000000000;
    unsigned long       N1 = 4294967290;
    long double sum = 0.0;
    for(unsigned long i = 1; i<=N1; i++) sum +=(1.0/i);
    for(unsigned long long i = N1+1; i<=N; i++) sum +=(1.0/i);