In this Kata we focus on finding a sum S(n) which is the total number of divisors taken for all natural numbers less or equal to n. More formally, we investigate the sum of n components denoted by d(1) + d(2) + ... + d(n) in which for any i starting from 1 up to n the value of d(i) tells us how many distinct numbers divide i without a remainder. 

Your solution should work for possibly large values of n without a timeout.
Assume n to be greater than zero and not greater than 999 999 999 999 999.
Brute force approaches will not be feasible options in such cases. It is fairly simple to conclude that for every n>1 there holds a recurrence S(n) = S(n-1) + d(n) with initial case S(1) = 1.

For example:
S(1) = 1
S(2) = 3
S(3) = 5
S(4) = 8
S(5) = 10

But is the fact useful anyway? If you find it is rather not, maybe this will help: 

Try to convince yourself that for any natural k, the number S(k) is the same as the number of pairs (m,n) that solve the inequality mn <= k in natural numbers.
Once it becomes clear, we can think of a partition of all the solutions into classes just by saying that a pair (m,n) belongs to the class indexed by n.
The question now arises if it is possible to count solutions of n-th class. If f(n) stands for the number of solutions that belong to n-th class, it means that S(k) = f(1) + f(2) + f(3) + ...

The reasoning presented above leads us to some kind of a formula for S(k), however not necessarily the most efficient one. Can you imagine that all the solutions to inequality mn <= k can be split using sqrt(k) as pivotal item?

```python

USER_FILENAME = "<user_code>"
import sys, json, builtins
import math, heapq, bisect, itertools, functools, collections, statistics, fractions, decimal, operator, array, random, re, string, os, pathlib
try:
    import resource as _res
except Exception:
    _res = None
from collections import Counter, defaultdict, deque, OrderedDict
from functools import lru_cache, reduce
from itertools import accumulate, permutations, combinations, product
from math import gcd, ceil, floor, sqrt
from decimal import Decimal
try:
    from typing import *
except Exception:
    pass
try:
    sys.setrecursionlimit(1_000_000)
except Exception:
    pass
try:
    import site as _site
    try:
        _sys_sites = _site.getsitepackages() if hasattr(_site, "getsitepackages") else []
        for _p in _sys_sites:
            if _p and _p not in sys.path:
                sys.path.append(_p)
    except Exception:
        pass
    try:
        _usp = _site.getusersitepackages()
        if isinstance(_usp, str):
            _usp = [_usp]
        for _p in _usp:
            if _p and _p not in sys.path:
                sys.path.append(_p)
    except Exception:
        pass
except Exception:
    pass

def _disabled_input(*args, **kwargs):
    raise RuntimeError("input() is disabled in callable mode")
builtins.input = _disabled_input

ns = {"__name__": "__judge__"}  # prevent if __name__ == "__main__" blocks
for _k, _v in list(globals().items()):
    if not _k.startswith("_"):
        ns[_k] = _v
_CODE = 'def count_divisors(n): # http://oeis.org/A006218\n    sq = int(n ** .5)\n    return 2 * sum(n // i for i in range(1, sq + 1)) - sq * sq'
_co = compile(_CODE, USER_FILENAME, "exec")
exec(_co, ns, ns)

_target = None
_fn_name = 'count_divisors'
if _fn_name:
    if "Solution" in ns:
        try:
            _obj = ns["Solution"]()
            if hasattr(_obj, _fn_name):
                _target = getattr(_obj, _fn_name)
        except Exception:
            _target = None
    if _target is None and _fn_name in ns and callable(ns[_fn_name]):
        _target = ns[_fn_name]
# Fallback: if there's exactly one user-defined function, use it
if _target is None:
    _cands = [v for k, v in ns.items() if callable(v) and getattr(v, "__module__", "") in ("__judge__", "__main__")]
    _user_funcs = [c for c in _cands if getattr(c, "__name__", "").startswith("_") is False]
    if len(_user_funcs) == 1:
        _target = _user_funcs[0]
if _target is None:
    raise RuntimeError(f"Could not resolve callable '{_fn_name}'")

_raw = sys.stdin.read().strip()
if _raw:
    _parsed = json.loads(_raw)
    if isinstance(_parsed, dict):
        _kwargs = _parsed.get("kwargs", {})
        _args = _parsed.get("args", [])
    else:
        _args, _kwargs = _parsed, {}
else:
    _args, _kwargs = [], {}
if not isinstance(_args, (list, tuple)):
    _args = [_args]
_res = _target(*_args, **_kwargs)
try:
    sys.stdout.write(repr(_res) + "\n")
except Exception:
    pass

```

Measured memory_bytes: 5496