Have you heard about Megamind? Megamind and Metro Man are two aliens who came to earth. Megamind wanted to destroy the earth, while Metro Man wanted to stop him and protect mankind. After a lot of fighting, Megamind finally threw Metro Man up into the sky. Metro Man was defeated and was never seen again. Megamind wanted to be a super villain. He believed that the difference between a villain and a super villain is nothing but presentation. Megamind became bored, as he had nobody or nothing to fight against since Metro Man was gone. So, he wanted to create another hero against whom he would fight for recreation. But accidentally, another villain named Hal Stewart was created in the process, who also wanted to destroy the earth. Also, at some point Megamind had fallen in love with a pretty girl named Roxanne Ritchi. This changed him into a new man. Now he wants to stop Hal Stewart for the sake of his love. So, the ultimate fight starts now.

* Megamind has unlimited supply of guns named Magic-48. Each of these guns has `shots` rounds of magic spells.
* Megamind has perfect aim. If he shoots a magic spell it will definitely hit Hal Stewart. Once hit, it decreases the energy level of Hal Stewart by `dps` units.
* However, since there are exactly `shots` rounds of magic spells in each of these guns, he may need to swap an old gun with a fully loaded one. This takes some time. Let’s call it swapping period. 
* Since Hal Stewart is a mutant, he has regeneration power. His energy level increases by `regen` unit during a swapping period. 
* Hal Stewart will be defeated immediately once his energy level becomes zero or negative. 
* Hal Stewart initially has the energy level of `hp` and Megamind has a fully loaded gun in his hand.
* Given the values of `hp`, `dps`, `shots` and `regen`, find the minimum number of times Megamind needs to shoot to defeat Hal Stewart. If it is not possible to defeat him,  return `-1` instead.

# Example
Suppose, `hp` = 13, `dps` = 4, `shots` = 3 and `regen` = 1. There are 3 rounds of spells in the gun. Megamind shoots all of them. Hal Stewart’s energy level decreases by 12 units, and thus his energy level becomes 1. Since Megamind’s gun is now empty, he will get a new gun and thus it’s a swapping period. At this time, Hal Stewart’s energy level will increase by 1 unit and will become 2. However, when Megamind shoots the next spell, Hal’s energy level will drop by 4 units and will become −2, thus defeating him. So it takes 4 shoots in total to defeat Hal Stewart. However, in this same example if Hal’s regeneration power was 50 instead of 1, it would have been impossible to defeat Hal.

```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 = 'from math import ceil\n\ndef mega_mind(hp, dps, shots, regen):\n    if hp > dps * shots <= regen:\n        return -1\n    n = 0\n    while True:\n        s = min(int(ceil(hp / dps)), shots)\n        n += s\n        hp -= dps * s\n        if hp <= 0:\n            break\n        hp += regen\n    return n'
_co = compile(_CODE, USER_FILENAME, "exec")
exec(_co, ns, ns)

_target = None
_fn_name = 'mega_mind'
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: 5552