Go: package main

import (
	"fmt"
	"math"
	"math/cmplx"
)

func main() {
	for {
		var n int
		fmt.Scan(&n)

		if n == 0 {
			return
		}

		arr := make([]complex128, n)

		for i := 0; i < n; i++ {
			var x, y float64

			fmt.Scanf("%f%f", &x, &y)

			arr[i] = complex(x, y)
		}

		max := 1
		for i := 0; i < n; i++ {
			for j := i + 1; j < n; j++ {
				sub := arr[j] - arr[i]

				if cmplx.Abs(sub) >= 2 {
					continue
				}
				sum := arr[j] + arr[i]

				v := 1
				{
					halfd := cmplx.Abs(sub / 2)

					center := sum/2 + sub*cmplx.Rect(math.Sqrt(1-halfd*halfd)/cmplx.Abs(sub), float64(v)*math.Pi/2)

					counter := 0
					for k := 0; k < n; k++ {
						if i == k || j == k || cmplx.Abs(arr[k]-center) <= 1 {
							counter++
						}
					}
					if max < counter {
						max = counter
					}
				}

				v = -1
				{
					halfd := cmplx.Abs(sub / 2)

					center := sum/2 + sub*cmplx.Rect(math.Sqrt(1-halfd*halfd)/cmplx.Abs(sub), float64(v)*math.Pi/2)

					counter := 0
					for k := 0; k < n; k++ {
						if i == k || j == k || cmplx.Abs(arr[k]-center) <= 1 {
							counter++
						}
					}
					if max < counter {
						max = counter
					}
				}

			}
		}

		fmt.Println(max)
	}
}

C++: #include <bits/stdc++.h>

using namespace std;

#define int long long
#define F first
#define S second
#define all(v) (v).begin(), (v).end()
#define rep(i, n) for(int i = 0; i < (int)(n); i++)
#define reps(i, f, n) for(int i = (int)(f); i < (int)(n); i++)
#define each(a, b) for(auto& a : b)

const int inf = 1LL << 55;

#define EPS (1e-10)
#define equals(a, b) (fabs((a)-(b)) < EPS)

// ???/????????????
struct Point {
  double x, y;
  Point(double x = 0.0, double y = 0.0):x(x), y(y){}
  
  Point operator + (Point p) { return Point(x + p.x, y + p.y); }
  Point operator - (Point p) { return Point(x - p.x, y - p.y); }
  Point operator * (double a) { return Point(x * a, y * a); }
  Point operator / (double a) { return Point(x / a, y / a); }

  double abs() { return sqrt(norm()); }
  double norm() { return x*x + y*y; }

  bool operator < (const Point& p) const {
    return x != p.x ? x < p.x : y < p.y;
  }
  bool operator == (const Point& p) const {
    return fabs(x - p.x) < EPS && fabs(y - p.y) < EPS;
  }
};
typedef Point Vector;

// ???
struct Circle {
  Point c;
  double r;
  Circle(Point c = Point(), double r = 0.0):c(c), r(r){}
};

// ????§???¢
typedef vector<Point> Polygon;

// ??????/??´???
struct Segment {
  Point p1, p2;
};
typedef Segment Line;

// ????????????????????????
double norm(Vector v)
{
  return v.x*v.x + v.y*v.y;
}
// ?????????????????§??????
double abs(Vector v)
{
  return sqrt(norm(v));
}
// ?????????????????????
double dot(Vector a, Vector b)
{
  return a.x*b.x + a.y*b.y;
}
// ??????????????????????????§??????
double cross(Vector a, Vector b)
{
  return a.x*b.y - a.y*b.x;
}
// ??´?????????
bool isOrthogonal(Vector a, Vector b)
{
  return equals(dot(a, b), 0.0);
}
bool isOrthogonal(Point a1, Point a2, Point b1, Point b2)
{
  return isOrthogonal(a1 - a2, b1 - b2);
}
bool isOrthogonal(Segment s1, Segment s2)
{
  return equals(dot(s1.p2 - s1.p1, s2.p2 - s2.p1), 0.0);
}
// ????????????
bool isParallel(Vector a, Vector b)
{
  return equals(cross(a, b), 0.0);
}
bool isParallel(Point a1, Point a2, Point b1, Point b2)
{
  return isParallel(a1 - a2, b1 - b2);
}
bool isParallel(Segment s1, Segment s2)
{
  return equals(cross(s1.p2 - s1.p1, s2.p2 - s2.p1), 0.0);
}
// ?°???±
Point project(Segment s, Point p)
{
  Vector base = s.p2 - s.p1;
  double r = dot(p - s.p1, base) / norm(base);
  return s.p1 + base * r;
}
// ????°?
Point reflect(Segment s, Point p)
{
  return p + (project(s, p) - p) * 2.0;
}
static const int COUNTER_CLOCKWISE = 1;
static const int CLOCKWISE         = -1;
static const int ONLINE_BACK       = 2;
static const int ONLINE_FRONT      = -2;
static const int ON_SEGMENT        = 0;
// ???????¨???????
int ccw(Point p0, Point p1, Point p2)
{
  Vector a = p1 - p0;
  Vector b = p2 - p0;
  if(cross(a, b) > EPS) return COUNTER_CLOCKWISE;
  if(cross(a, b) < -EPS) return CLOCKWISE;
  if(dot(a, b) < -EPS) return ONLINE_BACK;
  if(a.norm() < b.norm()) return ONLINE_FRONT;
  return ON_SEGMENT;
}
// ????????????
bool intersect(Point p1, Point p2, Point p3, Point p4)
{
  return (ccw(p1, p2, p3) * ccw(p1, p2, p4) <= 0 &&
	  ccw(p3, p4, p1) * ccw(p3, p4, p2) <= 0);
}
bool intersect(Segment s1, Segment s2)
{
  return intersect(s1.p1, s1.p2, s2.p1, s2.p2);
}
// ?????????????????¢
double getDistance(Point a, Point b)
{
  return abs(a - b);
}
// ??´?????¨?????¨????????¢
double getDistanceLP(Line l, Point p)
{
  return abs(cross(l.p2 - l.p1, p - l.p1) / abs(l.p2 - l.p1));
}
// ????????¨?????¨????????¢
double getDistanceSP(Segment s, Point p)
{
  if(dot(s.p2 - s.p1, p - s.p1) < 0.0) return abs(p - s.p1);
  if(dot(s.p1 - s.p2, p - s.p2) < 0.0) return abs(p - s.p2);
  return getDistanceLP(s, p);
}
// ????????????????????¢
double getDistance(Segment s1, Segment s2)
{
  if(intersect(s1, s2)) return 0.0;
  return min(min(getDistanceSP(s1, s2.p1), getDistanceSP(s1, s2.p2)),
	     min(getDistanceSP(s2, s1.p1), getDistanceSP(s2, s1.p2)));
}
// ???????????????
Point getCrossPoint(Segment s1, Segment s2)
{
  Vector base = s2.p2 - s2.p1;
  double d1 = abs(cross(base, s1.p1 - s2.p1));
  double d2 = abs(cross(base, s1.p2 - s2.p1));
  double t = d1 / (d1 + d2);
  return s1.p1 + (s1.p2 - s1.p1) * t;
}
// ???c??¨??????l?????????
pair<Point, Point> getCrossPoints(Circle c, Line l)
{
  // assert(intersect(c, l));
  Vector pr = project(l, c.c);
  Vector e = (l.p2 - l.p1) / abs(l.p2 - l.p1);
  double base = sqrt(c.r*c.r - norm(pr - c.c));
  return make_pair(pr + e * base, pr - e * base);
}
// ???c1??¨???c2?????????
double arg(Vector p) { return atan2(p.y, p.x); }
Vector polar(double a, double r) { return Point(cos(r) * a, sin(r) * a); }
pair<Point, Point> getCrossPoints(Circle c1, Circle c2)
{
  // assert(intersect(c1, c2));
  double d = abs(c1.c - c2.c);
  double a = acos((c1.r*c1.r + d*d - c2.r*c2.r) / (2*c1.r*d));
  double t = arg(c2.c - c1.c);
  return make_pair(c1.c + polar(c1.r, t + a), c1.c + polar(c1.r, t - a));
}
// ????????????
static const int IN_POLYGON = 2;
static const int ON_POLYGON = 1;
static const int OUT_POLYGON = 0;
int contains(Polygon g, Point p)
{
  int n = g.size();
  bool x = false;
  for(int i = 0; i < n; i++) {
    Point a = g[i] - p, b = g[(i+1) % n] - p;
    if(abs(cross(a, b)) < EPS && dot(a, b) < EPS) return ON_POLYGON;
    if(a.y > b.y) swap(a, b);
    if(a.y < EPS && EPS < b.y && cross(a, b) > EPS) x = !x;
  }
  return (x ? IN_POLYGON : OUT_POLYGON);
}

signed main()
{
  int N;
  while(cin >> N, N) {
    vector<Point> p(N);
    rep(i, N) cin >> p[i].x >> p[i].y;
    int ans = 0;
    rep(i, N) reps(j, i+1, N) {
      if(getDistance(p[i], p[j]) < 2.0 + EPS) {
	Circle c1(p[i], 1.0), c2(p[j], 1.0);
	auto cp = getCrossPoints(c1, c2);
	int cnt = 0;
	rep(k, N) if(getDistance(cp.first, p[k]) < 1.0 + EPS) cnt++;
	ans = max(ans, cnt);
	cnt = 0;
	rep(k, N) if(getDistance(cp.second, p[k]) < 1.0 + EPS) cnt++;
	ans = max(ans, cnt);
      }
    }
    cout << ans << endl;
  }
  return 0;
}