import arcpy
from arcpy import env

env.workspace = r"G:PROJECTSroad70-75"
counter = 0
for mxdname in arcpy.ListFiles("*.mxd"):
    print mxdname
    mxd = arcpy.mapping.MapDocument(
    r"G:PROJECTSroad70-75\" + mxdname)
    for elm in arcpy.mapping.ListLayoutElements(mxd, "TEXT_ELEMENT"):
        if elm.text.startswith(u'd'):
            elm.text = elm.text.replace(u'd', u'map num: ')[0]
            print 'elm.text','n'
            counter = counter + 1
    mxd.save()
del mxd
print 'total maps: ', counter