#include <iostream>
#include <algorithm>
#include <cstring>
#include <iomanip>
#include <cmath>

using namespace std;

const int N = 110, M = N * N * 2;
const double eps = 1e-7;

#define x first
#define y second

typedef pair<int,int> PII;

int l, w, n;
PII p[N];
int h[N], ne[M], e[M], idx;
bool st[N];

void add(int a, int b) {
    ne[idx] = h[a], e[idx] = b, h[a] = idx ++;
}

double get_dist(PII a, PII b) {
    double dx = a.x - b.x;
    double dy = a.y - b.y;
    return sqrt(dx * dx + dy * dy);
}

bool dfs(int u) {
    if (u == n + 1) return false;
    for (int i = h[u]; i != -1; i = ne[i]) {
        int j = e[i];
        if (!st[j]) {
            st[j] = true;
            if (!dfs(j)) return false;
        }
    }
    return true;
}

bool check(double mid) {
    memset(h, -1, sizeof(h));
    memset(st, false, sizeof(st));
    idx = 0;
    for (int i = 1; i <= n; i ++) {
        for (int j = i + 1; j <= n; j ++) {
            if (get_dist(p[i], p[j]) <= 2 * mid) add(i, j), add(j, i);
        }
    }
    for (int i = 1; i <= n; i ++) {
        if (p[i].y <= mid) add(0, i), add(i, 0);
        if (p[i].y >= w - mid) add(n + 1, i), add(i, n + 1);
    }
    st[0] = true;
    return dfs(0);
}

int main() {
    ios_base::sync_with_stdio(false);
    cin.tie(0), cout.tie(0);
    cin >> l >> w >> n;
    for (int i = 1; i <= n; i ++) {
        cin >> p[i].x >> p[i].y;
    }
    double l = 0 , r = 100;
    while (r - l > eps) {
        double mid = (l + r) / 2.0;
        if (check(mid)) l = mid;
        else r = mid;
    }
    cout << fixed << setprecision(6);
    cout << r << endl;
    
    return 0;
}