When the second intermediate period of egypt is the  ubaid period in mesopotamia how many early calcolithics are there?
create table table_23537091_1 (early_chalcolithic varchar, ubaid_period_in_mesopotamia varchar, PRIMARY KEY (early_chalcolithic))
select count(early_chalcolithic) from table_23537091_1 where ubaid_period_in_mesopotamia = "second intermediate period of egypt"