Asnail fell down a 50 feet deep well it crawls up 5 feet every day and slides down two feet each night. on which day will the snail leave the well

Day  Up  Down   Deep at the end of the day

1      5      2          50 - 3 = 47
2      5      2          50 - 6 = 44
3                          50 - 9 = 41
4                          50 - 12= 38
...
15                        50 - 15*3 = 5
16  5                    5 - 5 = 0  ´this day it leaves when goes up 5 feet and so does not go down the 2 feet

The snail will leave on the day 16th