Problem:
Projection

For given three points p1, p2, p, find the projection point x of p onto p1p2.

Input

xp1 yp1 xp2 yp2
q
xp0 yp0
xp1 yp1
...
xpq−1 ypq−1

In the first line, integer coordinates of p1 and p2 are given. Then, q queries are given for integer coordinates of p.

Output

For each query, print the coordinate of the projection point x. The output values should be in a decimal fraction with an error less than 0.00000001.

Constraints

1 ≤ q ≤ 1000

-10000 ≤ xi, yi ≤ 10000

p1 and p2 are not identical.

Sample Input 1

0 0 2 0
3
-1 1
0 1
1 1

Sample Output 1

-1.0000000000 0.0000000000
0.0000000000 0.0000000000
1.0000000000 0.0000000000

Sample Input 2

0 0 3 4
1
2 5

Sample Output 2

3.1200000000 4.1600000000

Solution in JAVA (judge verdict: Accepted)

import java.awt.geom.Point2D;
import java.util.*;
public class Main {
	Scanner in = new Scanner(System.in);
	public static void main(String[] args) {
		new Main();
	}
	public Main() {
		new AOJCGL_1().doIt();
	}

	class AOJCGL_1{
		void doIt(){
			Point2D p0 = new Point2D.Double(in.nextDouble(), in.nextDouble());
			Point2D p1 = new Point2D.Double(in.nextDouble(), in.nextDouble());
			int q = in.nextInt();
			for(int i=0;i<q;i++){
				Point2D result = getVerticalPoint(p0, p1, new Point2D.Double(in.nextDouble(),in.nextDouble()));
				System.out.printf("%.9f %.9f\n",result.getX(),result.getY());
			}
		}
		
		//p0-p1の直線があるときに直線p2から直線らしたときp0-p1上の垂直な点を求める。
		private Point2D getVerticalPoint(Point2D p0,Point2D p1,Point2D p2){
			double kyori = p0.distance(p1);
			double angle = angle(p0, p1, p2);
			double t = p0.distance(p2) * Math.cos(angle);
			Point2D result = new Point2D.Double(p0.getX()+(p1.getX()-p0.getX())*t/kyori,
					p0.getY()+(p1.getY()-p0.getY())*t/kyori);
			return result;
		}

		private double angle(Point2D p0, Point2D p1, Point2D p2){
			return Math.atan2(p2.getY()-p0.getY(),p2.getX()-p0.getX())-
					Math.atan2(p1.getY()-p0.getY(),p1.getX()-p0.getX());
		}

	}
}