N,M,K = map(int,input().split())
S = input()
now = 0
dat = [0] * 26
P = 998244353

dp = [[0] * 27 for _ in range(M + 1)]

ans = 0
for i in range(N):
    c = ord(S[i]) - ord('a')
    for j in range(c):
        if dat[j] == 0:
            dp[i + 1][now + 1] += 1
        else:
            dp[i + 1][now] += 1
    for j in range(27):
        dp[i + 1][j] += dp[i][j] * j
        if 0 < j < 26:
            dp[i + 1][j + 1] += dp[i][j] * (26 - j)
    for j in range(27):
        dp[i + 1][j] %= P
    if dat[c] == 0:
        now += 1
        dat[c] +=  1
    if now >= K:ans += 1

for i in range(N,M):
    for j in range(1,27):
        dp[i + 1][j] += dp[i][j] * j
        if 0 < j < 26:
            dp[i + 1][j + 1] += dp[i][j] * (26 - j)
    for j in range(27):
        dp[i + 1][j] %= P
    


for i in range(K,27):
    for j in range(M + 1):
        ans += dp[j][i]
if now >= K:ans -= 1
print(ans % P)