support product with integers across 0
support product with integers across 0

google/or-tools,google/or-tools,google/or-tools,or-tools/or-tools,google/or-tools,or-tools/or-tools,google/or-tools,or-tools/or-tools,or-tools/or-tools,or-tools/or-tools,or-tools/or-tools,google/or-tools