Convert number words to integer

Given a line containing an English phrase representing a number in the range −999,999,999 to 999,999,999, convert it to its integer value. Supported words: negative, zero, one, two, three, four, five, six, seven, eight, nine, ten, eleven, twelve, thirteen, fourteen, fifteen, sixteen, seventeen, eighteen, nineteen, twenty, thirty, forty, fifty, sixty, seventy, eighty, ninety, hundred, thousand, million. Negative numbers are prefixed with "negative". The word "hundred" is not used when "thousand" could be (e.g., 1500 is "one thousand five hundred"). Print the decimal representation for each input line. Examples: "fifteen" → 15; "negative six hundred thirty eight" → -638.