1966 IMO Problems/Problem 1

In a mathematical contest, three problems, , , and were posed. Among the participants ther were students who solved at least one problem each. Of all the contestants who did not solve problem , the number who solved was twice the number who solved . The number of students who solved only problem was one more than the number of students who solved and at least one other problem. Of all students who solved just one problem, half did not solve problem . How many students solved only problem ?