#include <bits/stdc++.h>
using namespace std;

#define endl '\n'
#define int long long
#define ull unsigned long long
typedef long long ll;
#define lowbit(x) ((x) & -(x))

const ll INF = 0x3f3f3f3f;
const ll mod = 998244353;
const int N = 1e6 + 5, M = 5e5 + 10;
typedef pair<int, int> PII;
double T = 1 >> 30;
// double PI = acos(-1);

int gcd(int a, int b)
{
    return b ? gcd(b, a % b) : a;
}

int lcm(int a, int b)
{
    return a / gcd(a, b) * b;
}

int h, w, n;
struct node
{
    double x, y;
} a[1005];

int fa[1010];

int find(int x)
{
    if (fa[x] != x)
    {
        fa[x] = find(fa[x]);
    }
    return fa[x];
}

void merge(int u, int v)
{
    u = find(u);
    v = find(v);
    if (u == v)
    {
        return;
    }
    fa[u] = v;
}

int ck(double r)
{
    for (int i = 1; i <= n + 4; i++)
    {
        fa[i] = i;
    }

    for (int i = 1; i <= n; i++)
    {
        double x = a[i].x, y = a[i].y;
        if (y + r > h)
        {
            merge(i, n + 1); // 上
        }
        if (y - r < 0)
        {
            merge(i, n + 2); // 下
        }
        if (x + r > w)
        {
            merge(i, n + 3); // 右
        }
        if (x - r < 0)
        {
            merge(i, n + 4); // 左
        }
        for (int j = 1; j < i; j++)
        {
            double dis = (a[j].x - x) * (a[j].x - x) + (a[j].y - y) * (a[j].y - y);
            if (dis < 4 * r * r)
            {
                merge(j, i);
            }
        }
    }

    if (find(n + 1) == find(n + 2) || find(n + 3) == find(n + 4) || find(n + 1) == find(n + 3) || find(n + 2) == find(n + 4))
    {
        return 0;
    }
    return 1;
}

void solve()
{
    int i, j;

    cin >> w >> h >> n;

    for (i = 1; i <= n; i++)
    {
        cin >> a[i].x >> a[i].y;
    }

    double l = 0, r = max(h, w);
    while (r - l >= 1e-6)
    {
        double mid = (l + r) / 2.0;
        if (ck(mid))
        {
            l = mid;
        }
        else
        {
            r = mid;
        }
    }

    cout << fixed << setprecision(6) << l;
}

signed main()
{
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr);
    cout.tie(nullptr);
    int t = 1;

    // cin >> t;

    while (t--)
    {
        solve();
    }

    //system("pause");
    return 0;
}