description: You are given a binary string (i. e. a string consisting of characters 0 and/or 1) s of length n. You can perform the following operation with the string s at most once: choose a substring (a contiguous subsequence) of s having exactly k characters 1 in it, and shuffle it (reorder the characters in the substring as you wish).
  
  Calculate the number of different strings which can be obtained from s by performing this operation at most once.
  
  Input
  
  The first line contains two integers n and k (2 ≤ n ≤ 5000; 0 ≤ k ≤ n).
  
  The second line contains the string s of length n, consisting of characters 0 and/or 1.
  
  Output
  
  Print one integer — the number of different strings which can be obtained from s by performing the described operation at most once. Since the answer can be large, output it modulo 998244353.
  
  Examples
  
  Input
  
  
  7 2
  1100110
  
  
  Output
  
  
  16
  
  
  Input
  
  
  5 0
  10010
  
  
  Output
  
  
  1
  
  
  Input
  
  
  8 1
  10001000
  
  
  Output
  
  
  10
  
  
  Input
  
  
  10 8
  0010011000
  
  
  Output
  
  
  1
  
  Note
  
  Some strings you can obtain in the first example:
  
    * to obtain 0110110, you can take the substring from the 1-st character to the 4-th character, which is 1100, and reorder its characters to get 0110; 
    * to obtain 1111000, you can take the substring from the 3-rd character to the 7-th character, which is 00110, and reorder its characters to get 11000; 
    * to obtain 1100101, you can take the substring from the 5-th character to the 7-th character, which is 110, and reorder its characters to get 101. 
  
  
  
  In the second example, k = 0 so you can only choose the substrings consisting only of 0 characters. Reordering them doesn't change the string at all, so the only string you can obtain is 10010.
solution: n,k=map(int, input().split())
  mod = 998244353
  
  s = input()
  
  facs = [1]
  ifacs = [1]
  for i in range(1, n+1):
      facs.append(facs[-1]*i % mod)
      ifacs.append(ifacs[-1]*pow(i, mod-2, mod) % mod)
  
  cc = sum([1 for c in s if c == '1'])
  
  ans = 1
  
  for i in range(n):
      c0, c1 = 0, 0
      for j in range(i, n):
          if s[j] == '1':
              c1+=1
          else:
              c0 +=1
          if c1 > k or cc < k:
              continue
          nc0, nc1 = c0, c1
          if s[i] == '1':
              nc0-=1
          else:
              nc1 -= 1
          if s[j] == '1':
              nc0 -=1
          else:
              nc1 -= 1
          if nc0 < 0 or nc1 < 0:
              continue
          assert nc0+nc1+2 == j-i+1
          ans += facs[nc0+nc1]*ifacs[nc1]*ifacs[nc0]
          ans %= mod
          # print(i, j, ans , nc0+nc1, nc1, ans)
  print(ans)
  