Once upon a time, on an island in the middle of an ocean, several tribes lived and fought with each other. A time came when all the tribes agreed to everlasting peace. So, they decided to build a giant monument to celebrate this Peace Treaty. The monument required a certain number of logs, and the tribes had to agree on the number of logs that each tribe was to provide. Had there been two fewer tribes on the island, this number of logs would have been 6. Had there been one more tribe on the island, this number would have been 5. Unfortunately, the tribes could not agree on what number of logs would be fair for the actual number of tribes. So the tribes announced an eternal war - and were not heard from ever again. How many tribes were on the island?