Go: package main

import (
	"bufio"
	"os"
	"math"
	"strings"
	"strconv"
	"fmt"
)

var scanner = bufio.NewScanner(os.Stdin)

const (
	INF = 0x7FFFFFFF
	EPS = 1e-10
)

type Point struct {
	x, y float64
}
func (p *Point) plus(q *Point) *Point {
	return &Point{p.x + q.x, p.y + q.y}
}
func (p *Point) minus(q *Point) *Point {
	return &Point{p.x - q.x, p.y - q.y}
}
func (p *Point) multi(a float64) *Point {
	return &Point{p.x * a, p.y * a}
}
func (p *Point) div(a float64) *Point {
	return &Point{p.x / a, p.y / a}
}
func (p *Point) abs() float64 {
	return math.Sqrt(p.norm())
}
func (p *Point) norm() float64 {
	return p.x*p.x + p.y*p.y
}
func (p *Point) isLessThan(q *Point) bool {
	if p.x != q.x {
		return p.x < q.x && p.y < q.y
	}
	return true
}
func (p *Point) isEqual(q *Point) bool {
	return math.Abs(p.x - q.x) < EPS && math.Abs(p.y - q.y) < EPS
}

type Segment struct {
	p1, p2 *Point
}
func (s *Segment) norm() float64 {
	return (s.p2.x - s.p1.x)*(s.p2.x - s.p1.x) +
		(s.p2.y - s.p1.y)*(s.p2.y - s.p1.y)
}
func (s *Segment) abs() float64 {
	return math.Sqrt(s.norm())
}

func norm(a *Point) float64 {
	return a.x*a.x + a.y*a.y
}

func abs(a *Point) float64 {
	return math.Sqrt(norm(a))
}

func polar(a, r float64) *Point {
	return &Point{math.Cos(r)*a, math.Sin(r)*a}
}

func getDistance(a, b *Point) float64 {
	return abs(a.minus(b))
}

func dot(a, b *Point) float64 {
	return a.x*b.x + a.y*b.y
}

func cross(a, b *Point) float64 {
	return a.x*b.y - a.y*b.x
}

func getDistanceLP(s Segment, p *Point) float64 {
	return cross(s.p2.minus(s.p1), p.minus(s.p1))/ abs(s.p2.minus(s.p1))
}

func getDistanceSP(s Segment, p *Point) float64 {
	if dot(s.p2.minus(s.p1), p.minus(s.p1)) < 0 {
		return abs(p.minus(s.p1))
	}
	if dot(s.p1.minus(s.p2), p.minus(s.p2)) < 0 {
		return abs(p.minus(s.p2))
	}
	return getDistanceLP(s, p)
}

func main() {
	for scanner.Scan() {
		buf := strings.Split(scanner.Text(), " ")
		R, _ := strconv.Atoi(buf[0])
		N, _ := strconv.Atoi(buf[1])
		if R == 0 && N == 0 {
			break
		}
		p := make([]*Point, N)
		r := make([]float64, N)
		v := make([]float64, N)
		d := make([]float64, N)
		nd := make([]float64, N)
		die := make([]bool, N)
		for i := 0; i < N; i++ {
			scanner.Scan()
			buf_ := strings.Split(scanner.Text(), " ")
			_x, _ := strconv.ParseFloat(buf_[0], 64)
			_y, _ := strconv.ParseFloat(buf_[1], 64)
			_r, _ := strconv.ParseFloat(buf_[2], 64)
			_v, _ := strconv.ParseFloat(buf_[3], 64)
			tmp := &Point{_x, _y}
			p[i] = tmp
			r[i] = _r
			v[i] = _v
			nd[i] = getDistance(p[i], &Point{0, 0})
			d[i] = getDistance(p[i], &Point{0, 0})
			die[i] = false
		}
		for {
			for i := 0; i < N; i++ {
				nd[i] = math.Max(float64(R), nd[i]-v[i])
			}
			mini := float64(INF)
			id := -1
			for i := 0; i < N; i++ {
				if die[i] {
					continue
				}
				if nd[i] < EPS+float64(R) {
					continue
				}
				if nd[i] > mini {
					continue
				}
				mini = nd[i]
				id = i
			}
			if id == -1 {
				break
			}
			s := Segment{p[id], p[id]}
			s.p1 = s.p1.div(d[id])
			s.p1 = s.p1.multi(float64(R))
			s.p2 = s.p2.div(d[id])
			s.p2 = s.p2.multi(10000000.0)
			for i := 0; i < N; i++ {
				if nd[i] < EPS + float64(R) {
					continue
				}
				a := p[i]
				a = a.div(d[i])
				a = a.multi(nd[i])
				if getDistanceSP(s, a) < EPS + r[i] {
					die[i] = true
				}
			}
		}
		ans := 0
		for i := 0; i < N; i++ {
			if !die[i] {
				ans++
			}
		}
		fmt.Println(ans)
	}
}

C++: #include<iostream>
#include<algorithm>
#include<cassert>
#include<map>
#include<vector>
#include<cmath>
#include<complex>
using namespace std;

#define REP(i,b,n) for(int i=b;i<n;i++)
#define rep(i,n)   REP(i,0,n)
#define N 100
#define DEAD false
#define ARRIVE true
#define eps 1e-10

typedef complex<double> P;

double dot(P a,P b){
  return a.real()*b.real()+a.imag()*b.imag();
}

double cross(P a,P b){
  return a.real()*b.imag()-a.imag()*b.real();
}

double distance_ls_p(P a,P b,P c,double r){
  if ( dot(b-a,c-a)<0)return r*2;
  else if ( dot(a-b,c-b)<0)return r*2;
  return abs(cross(b-a,c-a))/abs(b-a);
}


bool is_intersect_cl(P a,P b,P circle,double radius){
  bool flag1 = abs(a-circle)<=radius?1:0;
  bool flag2 = abs(b-circle)<=radius?1:0;
  
  if ( flag1 == true)return true;
  else if ( flag2 == true)return true;
  if (  distance_ls_p(a,b,circle,radius)<radius+eps)return true;
  return false;
}

class UFO{

public:
  P now;
  double r,v,theta,time;
  double vx,vy;
  bool flag;
  UFO(){};
  UFO(double tx,double ty,double tr,double tv,double R){
    flag = ARRIVE;
    now.real()=tx;
    now.imag()=ty;
    v=tv;
    r=tr;
    theta = arg(now);
    time = sqrt(tx*tx+ty*ty)-R;
    if (time < 0)flag=DEAD;
    else time/=v;
    vx=-cos(theta)*v;
    vy=-sin(theta)*v;    
  }

  void move(double t){    
    if (flag == DEAD){return;}
    now.real()+=vx;
    now.imag()+=vy;
    if ( time < t+eps){flag = DEAD;return ;}
  }

  bool crash_check(P a,P b){
    if ( flag == DEAD)return false;
    if ( is_intersect_cl(a,b,now,r)==true){
      flag = DEAD;
      return true;
    }
    return false;
  }
};


int solve(int n,UFO *data,double R){
  const double INF = 20000;
  int cnt=0;
  double time=1;
  while(true){
    double dist = 1000*1000;
    int minindex = -1;
    rep(i,n){
      data[i].move(time);
      if (data[i].flag == ARRIVE&& abs(data[i].now)<dist){
	dist=abs(data[i].now);
	minindex=i;
      }
    }
    if ( minindex == -1)break;
    
    P a,b,e;
    e = data[minindex].now/abs(data[minindex].now);
    a=e*R;
    b=e*INF;
    rep(i,n){
      if ( data[i].crash_check(a,b) == true)cnt++;
    }


    time+=1;
  }

  return n-cnt;
}

main(){
  double R;
  int n;
  while(cin>>R >> n && n){
    UFO data[n];
    rep(i,n){
      double x,y,r,v;
      cin>>x>>y>>r>>v;
      data[i]=UFO(x,y,r,v,R);
    }
    
    /*  

    for(double j=1;j<10;j+=1){
      cout <<j <<" seconds" << endl;
      rep(i,n){
	data[i].move(j);
	cout << data[i].flag <<" " <<data[i].time  << " " << data[i].now.real() <<" " << data[i].now.imag() << 
	  " " << abs(data[i].now) << " " << R << endl;

      }
      cout << "!!!"<<endl<<endl;
    }
*/
    cout << solve(n,data,R) << endl;

  }
}

C++: #include <iostream>
#include <cmath>
#include <algorithm>
#include <vector>
using namespace std;

#define EPS 1e-9

struct ufo {
	double x, y;
	double r, v;

	ufo() {}
	ufo(double x_, double y_, double r_, double v_) {
		x = x_; y = y_; r = r_; v = v_;
	}

	bool operator<(const ufo & obj) const {
		return x*x + y*y < obj.x*obj.x + obj.y*obj.y;
	}

	bool operator==(const ufo & obj) const {
		return x==obj.x && y==obj.y && r==obj.r && v==obj.v;
	}
};

int main() {
	int N, R;

	while(cin >> R >> N, R || N) {
		vector<ufo> u;
		for(int i = 0; i < N; i++) {
			double x, y, r, v;
			cin >> x >> y >> r >> v;
			u.push_back(ufo(x,y,r,v));
		}

		int ret = 0;
		int count = 0;
		while(!u.empty()) {
			for(int i = 0; i < u.size(); i++) {
				double x, y;
				x = u[i].x; y = u[i].y;
				x -= u[i].v * cos(atan2(u[i].y, u[i].x));
				y -= u[i].v * sin(atan2(u[i].y, u[i].x));
				u[i].x = x; u[i].y = y;
			}

			sort(u.begin(), u.end());
			ufo aim(0,0,0,0);
			for(int i = 0; i < u.size(); i++) {
				if(u[i].x*u[i].x + u[i].y*u[i].y < R*R + EPS) {
					u.erase(u.begin() + i);
					i--;
					ret++;
				}
				else {
					if(aim == ufo(0,0,0,0)) {
						aim = u[i];
						u.erase(u.begin() + i);
						i--;
					}
					else {
						double theta = (atan2(aim.y, aim.x)- atan2(u[i].y, u[i].x));
						double d0, d1, d2;
						d0 = sqrt(u[i].x*u[i].x + u[i].y*u[i].y);
						d1 = d0 * cos(theta);
						d2 = d0 * sin(theta);

						if(d2 < u[i].r + EPS && d1 > 0) {
							double d3;
							d3 = sqrt(u[i].r*u[i].r - d2*d2);
							if(d1 + d3 > R) {
								u.erase(u.begin() + i);
								i--;
							}
						}
					}
				}
			}
		}

		cout << ret << endl;
	}
}