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#include <bits/stdc++.h>

using namespace std;

template<typename T>
struct DSU {
    vector<T> sz, parent;
    int n;

    DSU(int n) : n(n) {
        sz = parent = vector<T>(n, 1);
        for (int i = 0; i < n; ++i) {
            parent[i] = i;
        }
    }

    int find(int x) {
        return parent[x] == x ? x : parent[x] = find(parent[x]);
    }

    void uni(int x, int y) {
        x = find(x), y = find(y);
        if (x == y)
            return;
        if (sz[x] < sz[y])
            swap(x, y);
        parent[y] = x;
        sz[x] += sz[y];
    }
};

int x, y;

struct pt {
    long double x, y;

    pt(long double x = 0, long double y = 0) : x(x), y(y) {};
};

bool overlap(pt p1, pt p2, long double r) {
    long double dist = (p1.x - p2.x) * (p1.x - p2.x) + (p1.y - p2.y) * (p1.y - p2.y);
    return dist < 4 * r * r;
}

bool in(pt p1, pt p2, long double r) {
    long double dist = (p1.x - p2.x) * (p1.x - p2.x) + (p1.y - p2.y) * (p1.y - p2.y);
    return dist < r * r;
}

bool touchWN(pt p1, long double r) {
    return in(p1, pt(0, p1.y), r) || in(p1, pt(p1.x, y), r);
}

bool touchES(pt p1, long double r) {
    return in(p1, pt(p1.x, 0), r) || in(p1, pt(x, p1.y), r);
}

int n;
vector<pt> v;

bool can(long double r) {
    DSU<int> dsu(n + 3);
    for (int i = 0; i < n; ++i) {
        if (touchES(v[i], r))
            dsu.uni(i, n);
        if (touchWN(v[i], r))
            dsu.uni(i, n + 1);
    }
    for (int i = 0; i < n; ++i) {
        for (int j = i + 1; j < n; ++j) {
            if (overlap(v[i], v[j], r)) {
                dsu.uni(i, j);
            }
        }
    }


    return dsu.find(n) != dsu.find(n + 1);
}

int main() {
    cin >> x >> y >> n;
    v.resize(n);
    for (int i = 0; i < n; ++i) {
        long double a, b;
        cin >> a >> b;
        v[i] = {a, b};
    }

    long double l = 0, r = 1e9, ans;
    while (r - l >= 1e-10) {
        long double mid = (l + r) / 2;
        if (can(mid)) {
            ans = mid;
            l = mid;
        } else {
            r = mid;
        }
    }

    cout << fixed << setprecision(5) << ans;

}