File ~/pandas-dev/pandas/core/tools/datetimes.py:1066, in to_datetime(arg, errors, dayfirst, yearfirst, utc, format, exact, unit, infer_datetime_format, origin, cache)
   1064         result = arg.map(cache_array)
   1065     else:
-> 1066         values = convert_listlike(arg._values, format)
   1067         result = arg._constructor(values, index=arg.index, name=arg.name)
   1068 elif isinstance(arg, (ABCDataFrame, abc.MutableMapping)):

File ~/pandas-dev/pandas/core/tools/datetimes.py:442, in _convert_listlike_datetimes(arg, format, name, utc, unit, errors, dayfirst, yearfirst, exact)
    439 require_iso8601 = format is not None and format_is_iso(format)
    441 if format is not None and not require_iso8601:
--> 442     return _to_datetime_with_format(
    443         arg,
    444         orig_arg,
    445         name,
    446         utc,
    447         format,
    448         exact,
    449         errors,
    450     )
    452 result, tz_parsed = objects_to_datetime64ns(
    453     arg,
    454     dayfirst=dayfirst,
   (...)
    461     exact=exact,
    462 )
    464 if tz_parsed is not None:
    465     # We can take a shortcut since the datetime64 numpy array
    466     # is in UTC

File ~/pandas-dev/pandas/core/tools/datetimes.py:543, in _to_datetime_with_format(arg, orig_arg, name, utc, fmt, exact, errors)
    540         return _box_as_indexlike(result, utc=utc, name=name)
    542 # fallback
--> 543 res = _array_strptime_with_fallback(arg, name, utc, fmt, exact, errors)
    544 return res

File ~/pandas-dev/pandas/core/tools/datetimes.py:485, in _array_strptime_with_fallback(arg, name, utc, fmt, exact, errors)
    481 """
    482 Call array_strptime, with fallback behavior depending on 'errors'.
    483 """
    484 try:
--> 485     result, timezones = array_strptime(
    486         arg, fmt, exact=exact, errors=errors, utc=utc
    487     )
    488 except OutOfBoundsDatetime:
    489     if errors == "raise":

File ~/pandas-dev/pandas/_libs/tslibs/strptime.pyx:198, in pandas._libs.tslibs.strptime.array_strptime()
    196         iresult[i] = NPY_NAT
    197         continue
--> 198     raise ValueError(f"time data '{val}' does not match "
    199                      f"format '{fmt}' (match)")
    200 if len(val) != found.end():

ValueError: time data '-9223372036854775808' does not match format '%Y%m' (match)