题目描述
Vasya had three strings $a$, $b$ and $s$, which consist of lowercase English letters. The lengths of strings $a$ and $b$ are equal to $n$, the length of the string $s$ is equal to $m$.
Vasya decided to choose a substring of the string $a$, then choose a substring of the string $b$ and concatenate them. Formally, he chooses a segment $[l_1, r_1]$ ($1 \leq l_1 \leq r_1 \leq n$) and a segment $[l_2, r_2]$ ($1 \leq l_2 \leq r_2 \leq n$), and after concatenation he obtains a string $a[l_1, r_1] + b[l_2, r_2] = a_{l_1} a_{l_1 + 1} \ldots a_{r_1} b_{l_2} b_{l_2 + 1} \ldots b_{r_2}$.
Now, Vasya is interested in counting number of ways to choose those segments adhering to the following conditions:
- segments $[l_1, r_1]$ and $[l_2, r_2]$ have non-empty intersection, i.e. there exists at least one integer $x$, such that $l_1 \leq x \leq r_1$ and $l_2 \leq x \leq r_2$;
- the string $a[l_1, r_1] + b[l_2, r_2]$ is equal to the string $s$.
Input
The first line contains integers $n$ and $m$ ($1 \leq n \leq 500\,000, 2 \leq m \leq 2 \cdot n$) — the length of strings $a$ and $b$ and the length of the string $s$.
The next three lines contain strings $a$, $b$ and $s$, respectively. The length of the strings $a$ and $b$ is $n$, while the length of the string $s$ is $m$.
All strings consist of lowercase English letters.
Output
Print one integer — the number of ways to choose a pair of segments, which satisfy Vasya's conditions.
输入格式
见题面 Input 部分
输出格式
见题面 Output 部分
样例输入
样例输出
提示
Let's list all the pairs of segments that Vasya could choose in the first example:
- $[2, 2]$ and $[2, 5]$;
- $[1, 2]$ and $[2, 4]$;
- $[5, 5]$ and $[2, 5]$;
- $[5, 6]$ and $[3, 5]$;