Present-day Slavic people are classified into West Slavic (chiefly Poles, Czechs and Slovaks), East Slavic (chiefly Russians, Belarusians, and Ukrainians), and South Slavic (chiefly Serbs, Bulgarians, Croats, Bosniaks, Macedonians, Slovenes, and Montenegrins), though sometimes the West Slavs and East Slavs are combined into a single group known as North Slavs. East Slavic people consist of which nationalities?