title: DFS and c-Expander graph - simple path with the length of n-2c+1
body: <p>Just to make it clear - c-Expander graph is a directed graph G(V,E) with 2 Disjoint sets (A and B), of size equal or more than c with at least one Vertex between node of A and node of B.</p>
  
  <p>I have to prove there is a simple directed path of length n-2c+1 in that graph.</p>
  
  <p>Any Ideas?</p>
  
  <p>(A tip I got - prove that when running DFS there is a stage the number of the Black nodes are equals to the number of the White nodes, where BLACK nodes are nodes we finished working on, and WHITE nodes are nodes we haven't started working on)</p>