Added reference to HackerRank Basic Programming Problem 'A very big sum'.
Added reference to HackerRank Basic Programming Problem 'A very big sum'.

shivkrthakur/HackerRankSolutions,shivkrthakur/HackerRankSolutions,shivkrthakur/HackerRankSolutions,shivkrthakur/HackerRankSolutions