public void reduce(Text key, Iterable<DoubleWritable> values,
				Context context) throws IOException, InterruptedException {
			long airportDistance = 0;
			for (DoubleWritable dis : values) {
				airportDistance += dis.get();
			}
			double sqrtDis = Math.sqrt(airportDistance);
			context.write(
					new Text(key.toString() + ","
							+ String.valueOf(sqrtDis)),
					NullWritable.get());
		}