Osogovo (Bulgarian and Macedonian Cyrillic:  Осогово (help·info)) or Osogovska Planina (Осоговска планина or Осоговски Планини) is a mountain and ski resort between southwestern Bulgaria (Kyustendil Province) and northeastern Republic of Macedonia, (Kočani and Kriva Palanka municipalities). It is about 110 km (68.35 mi) long and 50 km (31.07 mi) wide, the highest peak being Ruen (Руен) at 2251 m, which constitutes the main orthographic knot on the very border between Bulgaria and the Republic of Macedonia. The steepest slope of the mountain is in the west, stretching down from Carev Vrv (Царев Врв; "Tsar's Peak").