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"
ECHO: n = 4, x = 46, y = 79
ECHO: n = 3, x = 45, y = 78
ECHO: n = 2, x = 44, y = 77
ECHO: n = 1, x = 43, y = 76
ECHO: ftail_mixed = 42
