Run Kosaraju or Tarjan to find all SCCs. Count how many distinct SCCs exist. If there is exactly one SCC containing all n nodes, print "YES" (the graph is strongly connected). If there are two or more SCCs, print "NO" followed by two cities a and b in different SCCs.
It does not matter which pair you choose as long as they are in different components. Either a cannot reach b or b cannot reach a (or both).