Answer
$2445$
Work Step by Step
$M=1000
\\D=500
\\C=100
\\L=50
\\X=10
\\V=5$
Note that when a smaller number is written before a bigger number, the smaller number is subtracted to the bigger number.
Thus,
$MMCDXLV
\\= 1000+1000+(500-100)+(50-10)+5
\\= 2000+400+40+5
\\=2445$