10 9 5
0 0 0 0 0 0 0 0 0 4
10 3
10 7
10 5
10 8
10 9
10 1
10 4
10 6
10 2
 10 20 5
2 2 1 4 0 3 0 4 1 3
6 1
8 5
2 10
3 5
1 9
4 6
9 7
2 3
7 4
10 8
4 9
2 5
4 10
2 8
10 3
1 8
8 10
6 7
5 1
10 3
 10 9 2
1 1 0 1 1 1 1 1 1 1
3 10
3 8
3 6
3 7
3 5
3 4
3 1
3 9
3 2
 10 10 5
3 4 2 0 3 0 1 1 2 4
8 9
7 3
5 2
4 8
3 5
6 8
3 5
1 10
10 6
9 1
 10 30 10
7 9 1 5 4 6 0 3 8 2
10 8
8 5
6 1
8 5
3 10
10 8
9 2
8 5
7 3
3 10
1 9
10 8
6 1
1 9
8 5
7 3
1 9
7 3
7 3
4 6
10 8
7 3
3 10
10 8
1 9
8 5
6 1
4 6
3 10
6 1
 6 7 3
0 1 2 0 1 2
1 2
2 3
3 1
3 4
4 5
5 6
6 4
 10 9 2
0 1 0 0 1 0 1 1 1 1
3 7
3 2
8 6
1 7
3 9
5 4
10 1
4 9
6 2
 10 10 10
2 3 5 7 0 8 6 9 4 1
1 2
10 1
5 10
5 10
4 6
8 5
1 2
1 2
7 4
1 2
 10 9 5
1 1 1 1 1 2 1 1 1 1
6 7
6 3
6 5
6 4
6 9
6 8
6 1
6 10
6 2
 10 9 2
0 0 0 0 1 1 0 1 1 1
4 10
8 2
10 3
3 9
1 5
6 2
6 1
7 9
8 7
 5 5 3
2 2 0 1 0
5 4
5 2
1 4
5 1
4 3
 10 9 5
0 4 1 0 1 2 1 0 4 4
8 7
4 3
1 5
2 4
6 5
10 8
9 1
6 7
6 3
 7 8 3
0 0 1 2 2 0 1
1 5
4 3
7 5
1 7
3 2
2 4
6 7
6 5
 10 30 7
5 4 2 3 3 2 5 0 1 6
7 2
2 4
9 3
3 5
5 2
7 10
6 5
10 1
9 8
10 8
3 4
10 4
4 2
7 6
2 8
1 10
5 10
5 6
5 6
6 2
6 5
9 10
8 6
2 4
9 7
1 9
10 4
6 10
9 3
2 7
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1 1 2 0 0
1 3
1 5
2 3
3 4
2 4
 10 10 2
1 1 1 0 1 0 0 0 0 1
4 10
10 7
7 1
5 6
6 3
1 8
2 9
5 4
3 8
2 9
 9 13 3
0 2 1 2 2 0 1 0 1
4 7
9 5
7 5
7 6
9 6
8 2
3 2
8 3
4 3
4 9
1 2
1 3
5 6
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0 1 2 0 1 2
4 5
5 6
4 6
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3 3 3 4 4 1 3 0 2 4
7 5
10 8
10 8
5 8
2 10
9 2
7 4
3 4
7 5
4 8
 10 15 2
1 0 1 1 0 0 1 0 0 1
5 1
7 8
2 10
3 5
1 9
6 4
7 9
2 3
6 4
8 10
9 4
8 4
8 1
10 8
6 7
 2 1 2
1 0
1 2
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0 1 2 3 3
1 2
2 3
3 4
4 1
3 5
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2 1 2 0 1 0 1 2 0 4
10 9
3 7
1 5
10 6
7 9
10 4
5 4
2 6
8 2
 9 10 3
0 2 2 1 0 0 1 2 1
4 6
2 6
5 7
4 8
9 2
9 1
3 5
8 1
3 7
6 2
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2 2 1 1 2 0 0 1 2 2
7 5
7 10
2 7
10 4
10 8
1 7
3 7
9 7
3 10
6 3
4 1
4 1
8 6
3 7
10 3
2 7
8 5
2 7
1 4
2 6
 10 9 8
3 2 1 1 5 6 7 0 4 0
10 7
5 9
10 4
7 6
6 5
3 2
2 1
9 1
3 8

1
1 
 5
1 4 6 7 9 
 10
1 2 3 4 5 6 7 8 9 10 
 1
2 
 1
2 
 3
4 5 6 
 10
1 2 3 4 5 6 7 8 9 10 
 1
2 
 1
6 
 10
1 2 3 4 5 6 7 8 9 10 
 3
1 4 5 
 1
6 
 3
2 3 4 
 8
2 3 4 5 7 8 9 10 
 3
2 3 4 
 2
2 9 
 1
4 
 1
1 
 1
1 
 10
1 2 3 4 5 6 7 8 9 10 
 2
1 2 
 1
5 
 1
1 
 3
3 5 7 
 3
3 7 10 
 1
4 

#include <bits/stdc++.h>
using namespace std;
const long long INF = 1e18, CNT_IT = 1e5, MAX_COORD = 1e9;
const long double EPS = 1e-7;
struct Point {
  long long x, y;
  Point() {}
  Point(long long x, long long y) {
    this->x = x;
    this->y = y;
  }
  Point(Point p1, Point p2) {
    x = p2.x - p1.x;
    y = p2.y - p1.y;
  }
};
Point sp;
bool operator<(Point a, Point b) { return tie(a.x, a.y) < tie(b.x, b.y); }
bool operator==(Point a, Point b) { return tie(a.x, a.y) == tie(b.x, b.y); }
long long cp(Point a, Point b) { return a.x * b.y - a.y * b.x; }
long long dist2(Point a, Point b) {
  return (a.x - b.x) * (a.x - b.x) + (a.y - b.y) * (a.y - b.y);
}
bool cmp(Point a, Point b) {
  if (cp(Point(sp, a), Point(sp, b)) == 0) {
    return dist2(sp, a) < dist2(sp, b);
  }
  return cp(Point(sp, a), Point(sp, b)) > 0;
}
vector<Point> get_ch(vector<Point> points) {
  sort(points.begin(), points.end());
  auto last = unique(points.begin(), points.end());
  points.erase(last, points.end());
  sp = points[0];
  sort(points.begin(), points.end(), cmp);
  if ((signed)points.size() == 1) {
    return points;
  }
  vector<Point> ch = {points[0], points[1]};
  for (long long i = 2; i < (signed)points.size(); ++i) {
    while ((signed)ch.size() >= 2 &&
           cp(Point(ch[(signed)ch.size() - 2], ch.back()),
              Point(ch.back(), points[i])) <= 0) {
      ch.pop_back();
    }
    ch.push_back(points[i]);
  }
  return ch;
}
long long xrand() { return rand() * (1ll << 20) + rand(); }
signed main() {
  ios_base::sync_with_stdio(false);
  cin.tie(0);
  cout.tie(0);
  srand(4123);
  long long x, y, n;
  cin >> x >> y >> x >> y >> x >> y;
  cin >> n;
  long long cnt_ok = 0, cnt_all = 0;
  vector<Point> points(n);
  for (long long i = 0; i < CNT_IT; ++i) {
    for (long long j = 0; j < n; ++j) {
      long long x = xrand() % MAX_COORD, y = xrand() % (MAX_COORD - x);
      points[j] = Point(x, y);
    }
    vector<Point> ch = get_ch(points);
    if ((signed)ch.size() == n) {
      ++cnt_ok;
    }
    ++cnt_all;
  }
  long double ans = (long double)(cnt_ok) / cnt_all;
  cout.precision(30);
  cout << fixed << ans << endl;
  return 0;
}
