N=100000000
hsum: from 1 to 50000000 is 18.3047492182933
hsum: from 50000000 to 100000000 is 0.693147185559714
Main: hsum from 1 to 100000000 is 18.997896403853
time: 3.528 sec
Main: hsum from 1 to 100000000 is 18.9978964038527
time: 8.967 sec