George caught 300 fish and 10 wild boars. John grew 300 bunches of bananas. The 2 person economy that George & John set up, fish sell for 1 clamshell each, boars sell for 10 clamshell each, and bananas go for 5 clamshells a bunch. George paid John a total of 30 clamshells for helping him to dig bait for fishing, and he also purchased five of John's mature banana trees for 30 clamshells each. What is the GDP of George and John's island in terms of clamshells?