PRUNE  = 400
INPUT  = 'E13.04-Filtered.fens'
OUTPUT = INPUT.rstrip('fens') + '%dcp.fens'  % (PRUNE)

with open(INPUT, 'r') as fin:
    with open(OUTPUT, 'w') as fout:
        for line in fin:
            if abs(int(line.split()[-1])) <= PRUNE:
                fout.write(line)