You arrive at the train station in C-land, ready to explore the vast network of tunnels.

As you board one of the trains, you look ahead and see a long series of tunnels.

Each tunnel is labeled with a single letter and has exactly two ends.

You're given a sequence of tunnel labels (your puzzle input). Each tunnel is represented by a single uppercase or lowercase letter.

Each letter appears exactly twice, representing the two ends of a single tunnel.

Example Input:

ABccksiPiBAksP

This input contains seven different tunnels: A, B, c, k, s, i, and P.

The train starts at the first tunnel and moves through the sequence in the order the tunnels appear.

When it enters a tunnel, it instantly moves to the matching letter's position.

The number of steps taken inside a tunnel is equal to the number of characters between the two ends of that tunnel.

In the following diagram, arrows indicate the direction of travel between matching tunnel ends:

ABccksiPiBAksP
|---------^      // A -> A  (10 steps)
ABccksiPiBAksP
    ^------|     // k <- k  (7 steps)
ABccksiPiBAksP
     |------^    // s -> s  (7 steps)
ABccksiPiBAksP
       ^-----|   // P <- P  (6 steps)
ABccksiPiBAksP
      ^-|        // i <- i  (2 steps)
ABccksiPiBAksP
       |-----^   // P -> P  (6 steps, end of line)

The train moves forward or backward, depending on which tunnel it is currently in.

Counting the steps taken inside each tunnel, we get:"

A -> A  = 10 steps
k <- k  =  7 steps
s -> s  =  7 steps
P <- P  =  6 steps
i <- i  =  2 steps
P -> P  =  6 steps
------------------
Total   = 38 steps

Keep in mind that the step from one tunnel to the next is not counted. (outside the tunnel)

What is the total number of steps the train takes inside tunnels for the full map?