问题 C: Instructions Substring

**Red** stands at the coordinate $(0,0)$ of the Cartesian coordinate system. She has a string of instructions: up, down, left, right (where \`right' increases the x-coordinate by $1$, and \`up' increases the y-coordinate by $1$). Now **Red** wants to select a continuous substring of instructions and execute them. **Red** hopes that the final execution of the instructions can pass through the coordinate $(x,y)$. She wants to know how many selection options there are.

The first line contains three integers $n$, $x$, and $y$ $(1 \leq n \leq 2 \times 10^5, -10^5 \leq x, y \leq 10^5)$, — the length of the instruction string and the coordinates **Red** hopes to pass through. The second line contains a string of length $n$, consisting of the characters $'W'$, $'S'$, $'A'$, and $'D'$. — the four directions: up, down, left, and right, respectively.

Output one integer representing the number of selection options for the continuous substring.

Choosing $"AWDD"$, $"WD"$, or $"WDD"$ are all valid.