#P946F. Fibonacci String Subsequences
Fibonacci String Subsequences
Description
You are given a binary string s (each character of this string is either 0 or 1).
Let's denote the cost of string t as the number of occurences of s in t. For example, if s is 11 and t is 111011, then the cost of t is 3.
Let's also denote the Fibonacci strings sequence as follows:
- F(0) is 0;
- F(1) is 1;
- F(i) = F(i - 1) + F(i - 2) if i > 1, where + means the concatenation of two strings.
Your task is to calculate the sum of costs of all subsequences of the string F(x). Since answer may be large, calculate it modulo 109 + 7.
The first line contains two integers n and x (1 ≤ n ≤ 100, 0 ≤ x ≤ 100) — the length of s and the index of a Fibonacci string you are interested in, respectively.
The second line contains s — a string consisting of n characters. Each of these characters is either 0 or 1.
Print the only integer — the sum of costs of all subsequences of the string F(x), taken modulo 109 + 7.
Input
The first line contains two integers n and x (1 ≤ n ≤ 100, 0 ≤ x ≤ 100) — the length of s and the index of a Fibonacci string you are interested in, respectively.
The second line contains s — a string consisting of n characters. Each of these characters is either 0 or 1.
Output
Print the only integer — the sum of costs of all subsequences of the string F(x), taken modulo 109 + 7.
Samples
2 4
11
14
10 100
1010101010
553403224