def primesUpTo(n):
    ...

# Testing:
s = primesUpTo(1000)
print(s)

# Do some checks:
assert primesUpTo(30) == {2,3,5,7,11,13,17,19,23,29}
assert len(primesUpTo(1000)) == 168
assert len(primesUpTo(7918)) == 999
assert len(primesUpTo(7919)) == 1000
print("All tests passed!")