N,M,K=map(int, input().split())
S=input()
dp=[[0]*2 for i in range(28)]
dp[0][0]=1;T=[0]*26 

ans=0;mod=998244353
for j in range(N):
  ss=S[j]
  ndp=[[0]*2 for _ in range(28)]
  s=ord(ss)-ord('a')
  for i in range(27):
    ndp[i][1]+=dp[i][1]*i
    ndp[i][1]%=mod
    ndp[i+1][1]+=dp[i][1]*(26-i)
    ndp[i+1][1]%=mod
  t=sum(T)
  for i in range(s):
    if T[i]==0:
      ndp[t+1][1]+=dp[t][0]
      ndp[t+1][1]%=mod
    else:
      ndp[t][1]+=dp[t][0]
      ndp[t][1]%=mod
  if T[s]==0:
    ndp[t+1][0]+=dp[t][0]
    ndp[t+1][0]%=mod
  else:
    ndp[t][0]+=dp[t][0]
    ndp[t][0]%=mod
  T[s]=1
  dp=ndp
  for i in range(K,27):
    ans+=dp[i][0]
    ans+=dp[i][1]
    ans%=mod

for _ in range(M-N):
  ndp=[[0]*2 for _ in range(28)]
  for i in range(27):
    ndp[i][1]+=dp[i][1]*i
    ndp[i][1]%=mod
    ndp[i+1][1]+=dp[i][1]*(26-i)
    ndp[i+1][1]%=mod
  dp=ndp 
  for i in range(K,27):
    ans+=dp[i][0]
    ans+=dp[i][1]
    ans%=mod

print((ans-1)%mod)