Climb 1 10cm during the day, and descend by 40cm at night, which means climb 70cm every day, but you can climb 1 10cm on the last day.

If you ask for at least how deep it is, it should take a little more than 4 days to climb it.

Climb 3*70=2 10 in the first three days, 1 10 and ***320 on the fourth day, and climb for five days, at least a little more than 320 meters.

If you want to go deeper, the better. You should be able to climb 4 * 70 = 280m in the first four days,110m on the fifth day, * * * 390m, and one more day.

So this well is at least 320 meters deep (in fact, it is not only 320 meters, 320 meters only takes 4 days, it should be a little more than 320 meters).

It is as deep as 390 meters.