Language: C++

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

// ------ Classes ------ //
class Point {
public:
	long double px, py;
	Point() : px(0), py(0) {};
	Point(long double px_, long double py_) : px(px_), py(py_) {};
	bool operator==(const Point& p) const { return px == p.px && py == p.py; }
	bool operator!=(const Point& p) const { return px != p.px || py != p.py; }
	bool operator<(const Point& p) const { return px < p.px ? true : (px == p.px && py < p.py); }
	bool operator>(const Point& p) const { return px > p.px ? true : (px == p.px && py > p.py); }
	bool operator<=(const Point& p) const { return !(Point(px, py) > p); }
	bool operator>=(const Point& p) const { return !(Point(px, py) < p); }
	Point operator+(const Point& p) const { return Point(px + p.px, py + p.py); }
	Point operator-(const Point& p) const { return Point(px - p.px, py - p.py); }
	Point operator/(long double d) const { return Point(px / d, py / d); }
	friend Point operator*(const Point p, long double d) { return Point(p.px * d, p.py * d); }
	friend Point operator*(long double d, const Point& p) { return p * d; }
	Point& operator+=(const Point& p1) { px += p1.px, py += p1.py; return *this; }
	Point& operator-=(const Point& p1) { px -= p1.px, py -= p1.py; return *this; }
	Point& operator*=(long double d) { px *= d, py *= d; return *this; }
	Point& operator/=(long double d) { px /= d, py /= d; return *this; }
};
class Circle {
public:
	Point p; long double r;
	Circle() : p(Point()), r(0.0L) {};
	Circle(Point p_) : p(p_), r(0.0L) {};
	Circle(Point p_, long double r_) : p(p_), r(r_) {};
	Circle(long double x_, long double y_) : p(Point(x_, y_)), r(0.0L) {};
	Circle(long double x_, long double y_, long double r_) : p(Point(x_, y_)), r(r_) {};
	bool operator==(const Circle& c) const { return p == c.p && r == c.r; }
	bool operator!=(const Circle& c) const { return !(Circle(p, r) == c); }
};

// ------ Functions ------ //
long double norm(const Point& a) { return a.px * a.px + a.py * a.py; }
long double abs(const Point& a) { return sqrtl(norm(a)); }
long double arg(const Point& a) { return atan2l(a.py, a.px); }
long double dot(const Point& a, const Point& b) { return a.px * b.px + a.py * b.py; }
long double crs(const Point& a, const Point& b) { return a.px * b.py - a.py * b.px; }
Point pol(long double r, long double d) { return Point(cosl(d) * r, sinl(d) * r); }
int ccw(const Point& p0, const Point& p1, const Point& p2) {
	Point a = p1 - p0, b = p2 - p0;
	if (crs(a, b) > 1e-10) return 1;
	if (crs(a, b) < -1e-10) return -1;
	if (dot(a, b) < -1e-10) return 2;
	if (norm(a) < norm(b)) return -2;
	return 0;
}
bool its(const Point& p1, const Point& p2, const Point& p3, const Point& p4) { return (ccw(p1, p2, p3) * ccw(p1, p2, p4) <= 0 && ccw(p3, p4, p1) * ccw(p3, p4, p2) <= 0); }
long double dst(const Point& a, const Point& b) { return abs(b - a); }
vector<Point> crp(Circle c1, Circle c2) {
	double d = abs(c1.p - c2.p);
	double a = acos((c1.r * c1.r + d * d - c2.r * c2.r) / (2 * c1.r * d));
	double t = arg(c2.p - c1.p);
	return { c1.p + pol(c1.r, t + a), c1.p + pol(c1.r, t - a) };
}

// ------ Main ------ //
int n; char c; vector<Circle> v;
int main() {
	while (cin >> n, n) {
		v.resize(n);
		for (int i = 0; i < n; i++) cin >> v[i].p.px >> c >> v[i].p.py, v[i].r = 1;
		int ret = 0;
		for (int i = 0; i < n; i++) {
			for (int j = i + 1; j < n; j++) {
				vector<Point> w = crp(v[i], v[j]);
				for (int k = 0; k < 2; k++) {
					int s = 0;
					for (int l = 0; l < n; l++) {
						if (dst(w[k], v[l]) <= 1.0L + 1e-10) s++;
					}
					ret = max(ret, s);
				}
			}
		}
		cout << ret << endl;
	}
}

Compiler output:
a.cc: In function 'int main()':
a.cc:78:56: error: invalid initialization of reference of type 'const Point&' from expression of type '__gnu_cxx::__alloc_traits<std::allocator<Circle>, Circle>::value_type' {aka 'Circle'}
   78 |                                                 if (dst(w[k], v[l]) <= 1.0L + 1e-10) s++;
      |                                                     ~~~^~~~~~~~~~~~
a.cc:57:46: note: in passing argument 2 of 'long double dst(const Point&, const Point&)'
   57 | long double dst(const Point& a, const Point& b) { return abs(b - a); }
      |                                 ~~~~~~~~~~~~~^