Passage: To name a year using an era name only requires counting years from the first year of the era. For example, 138 BC was the third year of Jianyuan (建元), since 140 BC was the first year. When more than one monarch used the same motto, the name of the specific monarch or dynasty has to be mentioned. For instance both Emperor Wu and Jin Kangdi picked Jianyuan as their motto. Thus AD 344 was the second year of Jianyuan of the Jin Dynasty (or of Jin Kangdi) whereas 139 BC was the second year of Jianyuan of the Han Dynasty (or of Emperor Wu). In traditional literature, one can therefore find references like "the first month of the thirteenth year of Jianyuan" (建元十三年元月).

Question: Where does the counting begin when naming a year?
the first year of the era