86. Metro Stairs. Once, while exiting the "Kerli-street" metro station, we ran into a young athlete named Percy Longman. He stopped on the escalator and said:

- I always walk up the escalator. You know, extra training never hurts. This escalator is the longest on the line - almost a thousand steps. But here’s what’s interesting - and it applies to the other, smaller escalator I often have to climb: if, while climbing up, I step over two steps, the last step is one step; if I step over three steps, it’s two steps; if over four, it’s five steps; if over five, it’s four steps; if over six, it’s five steps; and finally, if I step over seven steps, the last step is six steps. I don’t know why this happens.

When Percy continued up, stepping over three steps at a time, we laughed, and my companion said:

- He probably doesn’t suspect that if he took steps of 20 steps, he would have 19 steps left on the last step!

How many steps are there on the escalator at the "Kerli-street" station, if the upper platform is counted as a step, but the lower one is not?*
86. The least common multiple of the numbers \(2,3,4,5,6\) and 7 is 420. Subtracting 1 from it, we get 419 - a possible number of steps. In addition, the conditions of the problem will be satisfied by numbers obtained by sequentially adding multiples of 420 to 419. Therefore, the number of steps in the escalator can be 419, \(839,1259,1679\) and so on. Since the escalator of interest contains fewer than 1000 steps and there is another escalator on the line with fewer steps, possessing the same properties as the first, the escalator at "Kerli-street" contains 839 steps.