#include <iostream>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <algorithm>
#include <cmath>
#include <vector>
#include <map>
#include <set>
#include <ctime>
#include <cassert>
#include <queue>

using namespace std;

#define f first
#define s second
#define mp make_pair
#define pb push_back
#define forit(it,con) for (typeof(con.begin()) it = con.begin(); it != con.end(); ++it)
#define f0(a) memset(a, 0, sizeof(a))
#define all(v) v.begin(), v.end()
#define pii pair<int,int>
#define vi vector<int>
#define ll long long

#ifdef WIN32
    #define I64 "%I64d"
#else
    #define I64 "%lld"
#endif
const double eps = 1e-12;
struct Point {
    double x, y, r;
    Point () {}

    Point(double xx, double yy) {
        x = xx; y = yy;
    }
    void read() {
        scanf("%lf%lf", &x, &y);
    }
    void readc() {
        scanf("%lf%lf%lf", &x, &y, &r);
    }
    Point operator - (Point a) {
        return Point(x - a.x, y - a.y);
    }
    Point operator + (Point a) {
        return Point(x + a.x, y + a.y);
    }
    double operator * (Point a) {
        return x * a.y - y * a.x;
    }
    void makeLen(double len) {
        double l = sqrt(x * x + y * y);
        x /= l; y /= l;
        x *= len; y *= len;
    }
    double scal(Point p) {
        return x * p.x + y * p.y;
    }
};
Point circ[1000000];
int n;
Point p, q;
pair<double, int> A[1000000];
int An;

int comp(double a,  double b) {
    if (fabs(a - b) < eps) return 0;
    if (a - b > eps) return 1;
    return -1;
}

void getLine(double &a, double &b, double &c, Point p, Point q) {
    a = p.y - q.y;
    b = q.x - p.x;
    c = -(a * p.x + b * p.y);
}

vector<Point> getInter(double a, double b, double c, Point circ) {
    vector<Point> ans;
    double dist = fabs(a * circ.x + b * circ.y + c);

    if (comp(dist, circ.r) >= 0) return ans;

    Point norm = Point(a, b);
    Point p;

    if (comp(a, 0) != 0) p = Point(-c / a, 0); else
    p = Point(0, -c / b);

    if (comp(norm.scal(circ - p), 0) > 0) norm.x *= -1, norm.y *= -1;
    norm.makeLen(dist);

    p = circ + norm;
    Point vec = Point(-b, a);
    vec.makeLen(sqrt(circ.r * circ.r - dist * dist));
    ans.pb(vec + p);
    ans.pb(p - vec);
    return  ans;
}
int main() {
    freopen("horseraces.in","r",stdin);
    freopen("horseraces.out","w",stdout);
    p.read(); q.read();
    scanf("%d", &n);
    for (int i = 0; i < n; ++i)
        circ[i].readc();
    double a, b, c;
    getLine(a, b, c, p, q);
    double d = sqrt(a * a + b * b);
    a /= d; b /= d; c /= d;

    Point dv = q - p;
    dv.makeLen(1);

    for (int i = 0; i < n; ++i) {
        vector<Point> tmp = getInter(a, b, c, circ[i]);
        if (tmp.size() != 2) continue;
        double t1, t2;
        if (comp(dv.x, 0) != 0) {
            t1 = (tmp[0].x - p.x) / dv.x;
            t2 = (tmp[1].x - p.x) / dv.x;
        } else {
            t1 = (tmp[0].y - p.y) / dv.y;
            t2 = (tmp[1].y - p.y) / dv.y;

        }
        if (comp(t1, t2) > 0) swap(t1, t2);

        A[An++] = mp(t1, 0);
        A[An++] = mp(t2, 1);
    }
    sort(A, A + An);
    int op = 0;
    double ans = 0;
    for (int i = 0; i < An; ++i) {
        if (op > 0) ans += A[i].f - A[i - 1].f;
        if (A[i].s == 0) ++op; else
        --op;
    }
    printf("%.6lf", ans);
    return 0;
}