class Pair implements Comparable<Pair> {
        int a;
        int b;

        Pair(int a, int b) {
            this.a = a;
            this.b = b;
        }

        @Override
        public int compareTo(Pair o) {
            if (ans * b - a - (ans * o.b - o.a) < 0) return -1;
            else return 1;
        }
    }

    double ans;

    void solve() throws IOException {
        int n = readInt();
        int k = readInt();
        int[] a = new int[n];
        int[] b = new int[n];
        double l = 0;
        double r = 1e10;
        for (int i = 0; i < n; i++) {
            a[i] = readInt();
            b[i] = readInt();
        }
        TreeSet<Pair> next = new TreeSet<>();
       int c = 200;
       while (c-->0){
            ans = (l + r) / 2;
            next.clear();
            for (int i = 0; i < n; i++) {
                next.add(new Pair(a[i], b[i]));
            }
            double ch = 0;
            double zn = 0;
            for (int i = 0; i < k; i++) {
                Pair next_ = next.pollFirst();
                ch += next_.a;
                zn += next_.b;
            }
            if (ch / zn >= ans) {
                l = ans;
            } else {
                r = ans;
            }
        }
        out.println(ans);
    }