ECHO: "without tail-recursion eliminiation: ", 5050
ECHO: "with tail-recursion eliminiation: ", 5050
ECHO: "with tail-recursion eliminiation: ", 2.001e+6
ECHO: [1980, 1980]
ECHO: 50000, "ACEGIKMOQSUWYACEGIKMOQSUWYACEGIKMOQSUWYA"
ECHO: 50000, "abcdefghijklmnopqrstuvwxyzabcdefghijklmn"
