In your program, you are over reading data from the file. Check Lego's answer, where he explains the mistake very clearly.
You can do it like this. This program assumes that the number of lines in the file is a multiple of 4.
with open("Input.txt", "r") as input_file:
for line1 in input_file:
line2, line3, line4 = [next(input_file) for _ in xrange(3)]
if "N" not in line2:
print line1 + line2 + line3 + line4.rstrip()
Output
@abcde:111/2
ABCDEFGHIj
+abcde:111/2
bla11
@abcde:113/2
djijwkoken
+abcde:113/2
bla15