input:
  question: A building has 10 floors. At the ground floor, 7 people enter the elevator.
    At the second floor, 3 people get off and 2 people enter. At the fourth floor,
    5 people get off and 2 people enter. At the seventh floor, 1 person gets off and
    3 people enter. Finally, at the tenth floor, everyone remaining in the elevator
    gets off. The question is, How many people were in the elevator when it started
    its journey, and how many total people exited the elevator by the end of its journey?
output: "The number of people in the elevator at any point can be modeled by adding
  the number of people who entered since the last time the elevator stopped at a floor,
  and subtracting the number of people who got off at that floor. \nWe start with
  7 people on the first floor, and then perform this operation at each floor:\n\n-
  On the second floor, 2 people enter and 3 people get off, so there are 7 + 2 - 3
  = 4 people in the elevator.\n- On the fourth floor, 2 people enter and 5 people
  get off, so there are 4 + 2 - 5 = 1 person in the elevator.\n- On the seventh floor,
  3 people enter and 1 person gets off, so there are 1 + 3 - 1 = 3 people in the elevator.\n-
  On the tenth floor, everyone remaining in the elevator gets off, so there are 3
  people in the elevator when it started its journey.\n\nThis is the same as the number
  of people who got off the elevator at each stop along the journey, so the answer
  is 3 + 3 = 6 people.\n\nTo find the number of people who entered the elevator, we
  can add the number of people who got off the elevator at each stop along the journey:
  7 + 4 + 1 + 3 = 15 people.\n\nTherefore, 15 people entered the elevator during its
  journey, and 6 people were in the elevator when it started its journey."