What are the names of the three nations where the longest river that empties into the Atlantic Ocean stretches to?
Empties into the Atlantic Ocean = flows to the Atlantic Ocean
SELECT DISTINCT T1.Country FROM city AS T1 INNER JOIN located AS T2 ON T1.Name = T2.City INNER JOIN river AS T3 ON T3.Name = T2.River WHERE T3.Name = ( SELECT Name FROM river WHERE Sea = 'Atlantic Ocean' ORDER BY Length DESC LIMIT 1 )