# Given an array S of n integers, are there elements a, b, c in S such that a + b + c = 0? Find all unique triplets in the array which gives the sum of zero.

# Note: The solution set must not contain duplicate triplets.

# For example, given array S = [-1, 0, 1, 2, -1, -4],

# A solution set is:
# [
#   [-1, 0, 1],
#   [-1, -1, 2]
# ]


add 15