MOD = 998244353

def code(s):
    return ord(s)-ord("a")
def codeR(n):
    return chr(ord("a")+n)

N, M, K = map(int, input().split())
S = input()

if N < M:
    S = S+"a"*(M-N)

F = [False]*26
dp = [[0]*27 for _ in range(M+1)]
ans = 0
for i in range(M):
    for j in range(27):
        dp[i+1][j] += dp[i][j]*j%MOD
        dp[i+1][j] %= MOD
        if j < 26:
            dp[i+1][j+1] += dp[i][j]*(26-j)%MOD
            dp[i+1][j+1] %= MOD
    cnt = sum(F)
    for j in range(code(S[i])):
        c = cnt+(F[j] == False)
        dp[i+1][c] += 1
        dp[i+1][c] %= MOD
    F[code(S[i])] = True
    if i+1 < N and K <= sum(F):
        ans += 1
        ans %= MOD

for i in range(M+1):
    ans += sum(dp[i][K:])
    ans %= MOD

print(ans)