String Graph Matching

You can build a graph from a string of lowercase letters as follows.

1. Create a vertex for each lowercase letter from a to z.
2. Write a string $S$ of length $L$ as $S_1S_2S_3\cdots S_L$. For every positive integer $i$ with $i \le L-1$, add the edge $S_i \to S_{i+1}$ to the graph. If the same edge would be added more than once, add it only once.

Given a graph whose vertices are the lowercase letters and a string $T$, count the substrings of $T$ that produce the same graph as the given graph through the process above.

A substring is a string of length at least $1$ obtained by cutting some number of characters from the front and some number from the back of a string. For example, for abcde, cd and abc are substrings, but bd is not, because no amount of cutting from the front and back yields it.

The first line contains an integer $N$, the length of the string ($2 \le N \le 2\,000\,000$).

The second line contains the string $T$, which consists only of lowercase letters and has length $N$.

The third line contains an integer $M$, the number of edges in the graph ($1 \le M \le 26^2$).

Each of the next $M$ lines contains two lowercase letters with no space between them. The line $x_iy_i$ denotes the directed edge $x_i \to y_i$. $x_i$ and $y_i$ may be the same letter. No edge is given more than once.

Print the number of substrings of $T$ that produce the same graph as the given graph through the process described above.