Vasya wants to climb up a stair of certain amount of steps (Input parameter 1). There are 2 simple rules that he has to stick to.

1. Vasya can climb 1 or 2 steps at each move.
2. Vasya wants the number of moves to be a multiple of a certain integer. (Input parameter 2).

### Task:
What is the `MINIMAL` number of moves making him climb to the top of the stairs that satisfies his conditions?

### Input

1. Number of stairs:    `0 <  N  ≤ 10000` ;
2. Integer to be multiplied : `1 < M ≤ 10 `;

### Output

1. Return a single integer - the minimal number of moves being a multiple of M;
2. If there is no way he can climb satisfying condition return - 1 instead. (`Nothing` in Haskell)

### Examples

```python
numberOfSteps(10, 2) => 6  # Sequence of steps : {2, 2, 2, 2, 1, 1}

numberOfSteps(3, 5) => -1 # !Possible sequences of steps : {2, 1}, {1, 2}, {1, 1, 1}
```
``` haskell
numberOfSteps 10 2 == Just 6  -- Sequence of steps : {2, 2, 2, 2, 1, 1}
numberOfSteps  3 5 == Nothing -- Not possible, since the sequences of steps would be {2, 1}, {1, 2} or {1, 1, 1}
```

```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;numberOfSteps=lambda s,m:next((i for i in range(ceil(s/2),s+1)if not i%m),-1)'
_co = compile(_CODE, USER_FILENAME, "exec")
exec(_co, ns, ns)

_target = None
_fn_name = 'numberOfSteps'
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: 5688