Which, and how many, of the Ecumenical Councils in Christendom does the Eastern Greek Orthodox Church accept as a basis for determining Doctrines?

The Eastern Orthodox Church (Greek Orthodox) considers ***(a) Scripture, (b) Tradition, and (c) Ecumenical Councils***, as a basis for determining and establishing doctrines (beliefs). However there are many Councils in the history of Christendom, with varied acceptance. Protestants generally accept the results of "the First Four." While the Roman Catholic religion accepts almost two dozen (21), and counting! How many does the Orthodox accept-along with its Holy Scriptures and Tradition of the Patristic Elders-for determining doctrines? And is there a ***reason(s)*** given for why only such a number? Would the Church accept the findings of a ***new Ecumenical Council***, if one were to be held in modern times?