#include <bits/stdc++.h>

using namespace std;

typedef long long ll;
typedef long double ld;

#define f first
#define sec second
#define mk make_pair
#define pb push_back
//#define int ll
#define all(x) x.begin(), x.end()

const int INF = 1e9 + 10;
const int N = 2e5 + 10;

struct st {
    ld f, t;
    int sec;
};

bool cmp(st a, st b) {
    return a.t < b.t || (a.t == b.t && a.sec > b.sec);
}

inline vector<st> unique(vector<st> &arr) {
    vector<st> res;
    res.pb(arr[0]);
    for (int i = 1; i < arr.size(); i++) {
        if (arr[i].f + arr[i].sec != res.back().f + res.back().sec) {
            res.pb(arr[i]);
        }
    }
    return res;
}

inline ld solve(vector<st> arr) {
    ld ans = -INF;
    sort(all(arr), cmp);
    arr = unique(arr);
    int n = arr.size();
    vector<ld> suf(n);
    suf[n - 1] = arr[n - 1].f - arr[n - 1].sec;
    for (int i = n - 2; i >= 0; i--) {
        suf[i] = min(suf[i + 1], arr[i].f - arr[i].sec);
    }
    for (int i = 0; i + 1 < arr.size(); i++) {
        ans = max(ans, suf[i + 1] - (arr[i].f + arr[i].sec));
    }
    if (ans < 0) {
        cout << -1;
        exit(0);
    }
    else {
        return ans;
    }
}

signed main() {
#ifdef HOME
    freopen("input.txt", "r", stdin);
    //freopen("output.txt", "w", stdout);
#endif
    cin.tie(0);
    cout.tie(0);
    ios_base::sync_with_stdio(0);
    ld x1, x2, y1, y2;
    cin >> x1 >> y1 >> x2 >> y2;
    if (x1 == x2) {
        int n;
        cin >> n;
        vector<st> arr(n);
        for (int i = 0; i < n; i++) {
            cin >> arr[i].f >> arr[i].sec >> arr[i].sec;
            arr[i].t = arr[i].f + arr[i].sec;
        }
        cout << fixed << setprecision(10) << solve(arr);
    }
    else if (y1 == y2) {
        int n;
        cin >> n;
        vector<st> arr(n);
        for (int i = 0; i < n; i++) {
            cin >> arr[i].f >> arr[i].f >> arr[i].sec;
            arr[i].t = arr[i].f + arr[i].sec;
        }
        cout << fixed << setprecision(10) << solve(arr);
    }
    else {
        ld k = (y2 - y1) / (x2 - x1);
        ld a = 1, b = abs(-1.0 / k), c = sqrt(a * a + b * b), d = abs(a * b / c);
        int n;
        cin >> n;
        vector<st> arr(n);
        for (int i = 0; i < n; i++) {
            ld x, y, r;
            cin >> x >> y >> r;
            arr[i].f = (y - k * x) * d;
            arr[i].sec = r;
            arr[i].t = arr[i].f + arr[i].sec;
        }
        cout << fixed << setprecision(10) << solve(arr);
    }
    return 0;
}