Spider

3000ms

262144K

Description:

A plane contains a not necessarily convex polygon without self-intersections, consisting of n vertexes, numbered from 1 to n. There is a spider sitting on the border of the polygon, the spider can move like that:

Transfer. The spider moves from the point p₁ with coordinates (x₁, y₁), lying on the polygon border, to the point p₂ with coordinates (x₂, y₂), also lying on the border. The spider can't go beyond the polygon border as it transfers, that is, the spider's path from point p₁ to point p₂ goes along the polygon border. It's up to the spider to choose the direction of walking round the polygon border (clockwise or counterclockwise).
Descend. The spider moves from point p₁ with coordinates (x₁, y₁) to point p₂ with coordinates (x₂, y₂), at that points p₁ and p₂ must lie on one vertical straight line (x₁ = x₂), point p₁ must be not lower than point p₂ (y₁ ≥ y₂) and segment p₁p₂ mustn't have points, located strictly outside the polygon (specifically, the segment can have common points with the border).

Initially the spider is located at the polygon vertex with number s. Find the length of the shortest path to the vertex number t, consisting of transfers and descends. The distance is determined by the usual Euclidean metric $\text{[math]}$ .

Input:

The first line contains integer n (3 ≤ n ≤ 10⁵) — the number of vertexes of the given polygon. Next n lines contain two space-separated integers each — the coordinates of the polygon vertexes. The vertexes are listed in the counter-clockwise order. The coordinates of the polygon vertexes do not exceed 10⁴ in their absolute value.

The last line contains two space-separated integers s and t (1 ≤ s, t ≤ n) — the start and the end vertexes of the sought shortest way.

Consider the polygon vertexes numbered in the order they are given in the input, that is, the coordinates of the first vertex are located on the second line of the input and the coordinates of the n-th vertex are on the (n + 1)-th line. It is guaranteed that the given polygon is simple, that is, it contains no self-intersections or self-tangencies.

Output:

In the output print a single real number — the length of the shortest way from vertex s to vertex t. The answer is considered correct, if its absolute or relative error does not exceed 10^- 6.

Sample Input:

Sample Output:

1.000000000000000000e+000

Sample Input:

Sample Output:

0.000000000000000000e+000

Sample Input:

Sample Output:

5.650281539872884700e+000

Note:

In the first sample the spider transfers along the side that connects vertexes 1 and 4.

In the second sample the spider doesn't have to transfer anywhere, so the distance equals zero.

In the third sample the best strategy for the spider is to transfer from vertex 3 to point (2,3), descend to point (2,1), and then transfer to vertex 1.

Informação

Provedor Codeforces

Código CF223D