N, M, K = map(int, input().split())
S = [ord(s) - ord("a") for s in input()]
mod = 998244353

num = 27
pre = [0] * num
SS = set()
ans = 0
for i in range(M):
    dp = [0] * num
    for j in range(num):
        if j == len(SS) and i <= N - 1:
            for k in range(S[i]):
                if k in SS:
                    dp[j] += 1
                else:
                    dp[j + 1] += 1
                
        dp[j] += pre[j] * j
        dp[j] %= mod
        if j != num - 1:
            dp[j + 1] += pre[j] * (26 - j)
            dp[j + 1] %= mod
            
    if i <= N - 1:
        SS.add(S[i])
    if len(SS) >= K and i < N - 1:
        ans += 1
    ans += sum(dp[K:])
    ans %= mod
    pre, dp = dp, pre
    
print(ans)