removeFirst(0, "rabbit") = "rabbit" removeFirst(1, "rabbit") = "abbit" removeFirst(2, "rabbit") = "bbit" removeFirst(3, "rabbit") = "bit" removeFirst(4, "rabbit") = "it" removeFirst(5, "rabbit") = "t" removeFirst(6, "rabbit") = "" removeFirst(7, "rabbit") = "" removeFirst(2, "abcd") = "cd" removeFirst(5, "") = ""