Calculati suma: 5 + 10 + 15 + ... + 2005 + 2010 + 2015.
5 = 5 * 1 10 = 5 * 2; ... 2015 = 5 * 403
Suma = 5 (1 + 2 + ... + 403) = 5 * (403 * 404) / 2 = 407030.