n,m,k=map(int,input().split())
K=26
s=input()
s=[ord(c)-ord("a") for c in s]
q=[0]*(K+1)
a=0
M=998244353
c=[0]*K
for i in range(m):
  nq=[0]*(K+1)
  for j in range(1,K+1):
    nq[j]+=q[j]*j
    if j<K:
      nq[j+1]+=q[j]*(K-j)
  g=sum(c)
  if i<n:
    for j in range(s[i]):
      if c[j]:
        nq[g]+=1
      else:
        nq[g+1]+=1
    c[s[i]]=1
  q=nq
  for j in range(1,K+1):
    q[j]%=M
  a+=i<n-1 and sum(c)>=k
  a+=sum(q[k:])
  a%=M
print(a)