Read the poem "Travel" by Edna St. Vincent Millay.The railroad track is miles away,And the day is loud with voices speaking,Yet there isn't a train goes by all dayBut I hear its whistle shrieking. All night there isn't a train goes by,Though the night is still for sleep and dreaming,But I see its cinders red on the sky,And hear its engine steaming. My heart is warm with friends I make,And better friends I'll not be knowing;Yet there isn't a train I wouldn't take,No matter where it's going.What is the central idea of this poem?