Merge converted results to one text file

Example:

cat 1.smi | perl smi_millisecond2csv.pl >> converted.txt
cat 2.smi | perl smi_millisecond2csv.pl >> converted.txt
cat 3.smi | perl smi_millisecond2csv.pl >> converted.txt
cat 4.smi | perl smi_millisecond2csv.pl >> converted.txt