Consider the following array:

```
[1, 12, 123, 1234, 12345, 123456, 1234567, 12345678, 123456789, 12345678910, 1234567891011...]
```

If we join these blocks of numbers, we come up with an infinite sequence which starts with `112123123412345123456...`. The list is infinite.

You will be given an number (`n`) and your task will be to return the element at that index in the sequence, where `1 ≤ n ≤ 10^18`. Assume the indexes start with `1`, not `0`.  For example:

```
solve(1) = 1, because the first character in the sequence is 1. There is no index 0. 
solve(2) = 1, because the second character is also 1.
solve(3) = 2, because the third character is 2.
```

More examples in the test cases. Good luck!

```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 getGreatest(n, d, prefix):\n    rows = 9 * 10**(d - 1)\n    triangle = rows * (d + rows * d) // 2\n    l = 0\n    r = triangle\n    \n    while l < r:\n        mid = l + ((r - l) >> 1)\n        triangle = mid * prefix + mid * (d + mid * d) // 2\n        prevTriangle = (mid-1) * prefix + (mid-1) * (d + (mid-1) * d) // 2\n        nextTriangle = (mid+1) * prefix + (mid+1) * (d + (mid+1) * d) // 2\n        if triangle >= n:\n            if prevTriangle < n:\n                return prevTriangle\n            else:\n                r = mid - 1\n        else:\n            if nextTriangle >= n:\n                return triangle\n            else:\n                l = mid\n        \n    \n    return l * prefix + l * (d + l * d) // 2\n\nns = [\n  1, # 1\n  2, # 1\n  3, # 2\n  100, # 1\n  2100, # 2\n  31000, # 2\n  999999999999999999, # 4\n  1000000000000000000, # 1\n  999999999999999993, # 7\n]\n\n\ndef solve(n):\n    debug = 1\n    d = 0\n    p = 0.1\n    prefixes = [0]\n    sections = [0]\n    \n    while sections[d] < n:\n        d += 1\n        p *= 10\n        rows = int(9 * p)\n        triangle = rows * (d + rows * d) // 2\n        section = rows * prefixes[d-1] + triangle\n        sections.append(sections[d-1] + section)\n        prefixes.append(prefixes[d-1] + rows * d)\n        \n    section = sections[d - 1]\n    n = n - section\n    rows = getGreatest(n, d, prefixes[d - 1])\n    \n    n = n - rows\n    d = 1\n    while prefixes[d] < n:\n        d += 1;\n        \n    if prefixes[d] == n:\n        return 9;\n    \n    prefix = prefixes[d - 1]\n    n -= prefix\n    countDDigitNums = n // d\n    remainder = n % d\n    prev = 10**(d - 1) - 1\n    num = prev + countDDigitNums\n    \n    if remainder:\n        return int(str(num + 1)[remainder - 1])\n    else:\n        s = str(num);\n        return int(s[len(s) - 1])'
_co = compile(_CODE, USER_FILENAME, "exec")
exec(_co, ns, ns)

_target = None
_fn_name = 'solve'
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: 6512