nums.py

from sys import stdin, stdout

value = None
for line in stdin:
    if line.startswith("t="):
        value = int(line[2:]) / 1000.0
        break
if value:
    stdout.write("{0},\n".format(value))

# On linux: "cat foo|python nums.py >>data.csv"
# On windows: "type foo.txt|python nums.py >>data.csv"