//  revised version of ComputePerimeter where the points are input from a disk file

import java.io.*;				// needed for File and IOException
import java.util.Scanner;

public class ComputePerimeter2
{
	public static void main(String[] args) throws IOException
	{
		int[][] points = getInput();
		int n = points.length;
		double sum = 0.0;
		for(int i=0;i<n;i++)		
			sum+=distance(points, i, n);
		System.out.printf("This polygon of %d points has a perimeter of %7.2f", n, sum);
	}
	
	public static int[][] getInput() throws IOException		// method to input the data points of our polygon from a file
	{
		Scanner in = new Scanner(new File("points.dat"));
		int[][] temp = new int[100][2];				// assume the file won't have more than 100 points
		int count = 0;								// count will count the number of inputs, used to control access into the array and to later copy the array into another array
		while(in.hasNext()&&count<100)
		{
			temp[count][0] = in.nextInt();			// get the x-coordinate for point count
			temp[count][1] = in.nextInt();			// get the y-coordinate for point count
			count++;								// we have now input the count value, go on to the next one
		}
		int[][] temp2 = new int[count][2];			// as temp is 100x2, if count < 100, we should reduce its size
		for(int i=0;i<count;i++) {					// copy each element of the temp array into the temp2 array whose size is exactly what we need
			temp2[i][0] = temp[i][0];
			temp2[i][1] = temp[i][1];
		}
		return temp2;								// return the smaller sized array
	}
	
	public static double distance(int[][] p, int i, int n)			// when i==n-1, we are on the last point, use point 0 as the other point
	{
		int x1 = p[i][0], y1 = p[i][1];
		int x2, y2;
		if(i==n-1) {
			x2 = p[0][0];
			y2 = p[0][1];
		}
		else {
			x2 = p[i+1][0];
			y2 = p[i+1][1];
		}
		return Math.sqrt((x1-x2)*(x1-x2) + (y1-y2)*(y1-y2));
	}
}