In a mathematical contest, three problems, A, B and C were posted. Among the participants there were 25 students who solved at least one problem each. Of all the contestants who didn’t solved problem A, the number who solved B was twice the number who solved C. The number of students who solved only problem A was one more than the number of students who solved A and at least one other problem. Of all students who solved just one problem, half didn’t solve problem A. How many students solved only problem B?