if each year the population of the country grows by 20 % , how many years will elapse before the population of the country doubles ?
"till year 2000 , population is 100 . year 2001 : population becomes 120 . . . . . . . . . . . . . 1 year elapsed year 2002 : population becomes 144 . . . . . . . . . . . . . 2 year elapsed year 2003 : population becomes 172 . . . . . . . . . . . . . 3 year elapsed year 2004 : population > 200 . . . . . . . . . . . . . . . . . . 4 year elapsed answer : b"
add(const_4, const_4)