To conjugate a verb ending in -er, as in correr, what would you do first?

add the verb endings -o, -as, -a, -amos, -áis, or -an to the stem.
drop the -rer from the infinitive, leaving the stem cor.
add the verb endings -o, -as, -e, -emos, -áis, or -an to the stem.
drop the -er from the infinitive, leaving the stem corr