#include <iostream>
#include <complex>
#include <cmath>
#include <vector>
#include <cstdio>

using namespace std;

double distance(double x0, double y0, double x1, double y1)
{
	const double x = x0 - x1;
	const double y = y0 - y1;
	return sqrt(x * x + y * y);
}

bool go(vector<vector<pair<int, double> > >& graph, double r)
{
	const int n = graph.size();
	const int leftNode = n - 2;
	const int rightNode = n - 1;
	vector<int> open;
	open.push_back(leftNode);
	vector<int> memo(n);
	memo[leftNode] = true;

	while (!open.empty() && !memo[rightNode]){
		const int current = open.back();
		open.pop_back();

		for (vector<pair<int, double> >::iterator it = graph[current].begin(); it != graph[current].end(); ++it){
			const int next = it->first;
			const double cost = it->second;
			if (!memo[next] && cost < r){
				open.push_back(next);
				memo[next] = true;
			}
		}
	}

	return memo[rightNode] != 0;
}

int main()
{
	for (int W, H, N; cin >> W >> H >> N && W && H && N;){
		const int leftNode = N;
		const int rightNode = N + 1;

		vector<int> xs;
		vector<int> ys;
		for (int i = 0; i < N; ++i){
			int x, y;
			cin >> x >> y;
			xs.push_back(x);
			ys.push_back(y);
		}

		vector<vector<pair<int, double> > > graph(N + 2);

		for (int i = 0; i < N; ++i){
			for (int j = i + 1; j < N; ++j){
				const double r = distance(xs[i], ys[i], xs[j], ys[j]);
				graph[i].push_back(make_pair(j, r * 0.5));
				graph[j].push_back(make_pair(i, r * 0.5));
			}
		}

		for (int i = 0; i < N; ++i){
			graph[leftNode].push_back(make_pair(i, xs[i]));
			graph[i].push_back(make_pair(leftNode, xs[i]));
			graph[i].push_back(make_pair(rightNode, W - xs[i]));
			graph[rightNode].push_back(make_pair(i, W - xs[i]));
		}

		double l = 0;
		double r = 1e10;
		for (int loop = 0; loop < 100; ++loop){
			const double m = (l + r) * 0.5;
			if (go(graph, m)){
				r = m;
			} else {
				l = m;
			}
		}

		const double m = (l + r) * 0.5;
		printf("%.20lf\n", m);
	}
}