• محدودیت زمان: ۲ ثانیه
• محدودیت حافظه: ۲۵۶ مگابایت

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There are $n$ wooden rods vertically placed over a horizontal line. The rods are numbered $1$ through $n$ from left to right. Each rod $i$ ($1 \leq i \leq n$) is placed at position $x_i$ and has a height $h_i$.

A termite wants to eat all the rods one by one. It starts eating from an arbitrary rod $s$ ($1 \leq s \leq n$). Then, after eating a rod $i$, the termite selects the next rod to eat based on the following method. Among the remaining rods $j$, the one with maximum $h_j - |x_i - x_j |$ is selected. If there are ties, the one with minimum $|x_i - x_j |$ is selected. If there are still ties, the left-most rod is selected.

Your task is to calculate the total (horizontal) distance traveled by the termite to eat all the rods.

ورودی

The first line of the input contains two space-separated integers $n$, the number of rods, and $s$, the starting rod number ($1 \leq s \leq n \leq 100, 000$). The rods are described in the next $n$ lines. On the line $1 + i$ ($1 \leq i \leq n$), the $i$-th rod is specified with two space-separated integers $x_i$ ($|x_i | \leq 10^9$) and $h_i$ ($1 \leq h_i \leq 10^9$). Additionally, for each $i$ ($1 \leq i \leq n - 1$), $x_i \lt x_{i+1}$.

خروجی

You should print a single integer denoting the total distance traveled by the termite.

مثال

ورودی نمونه ۱

5 3
1 3
4 8
8 2
10 4
11 1

خروجی نمونه ۱

17