n,m,k = map(int,input().split())
s = [ord(si) - ord('a') for si in input()]

seen = [False] * 27
dp = [0] * 27
dp[0] = 1
used = 0
ans = 0

for i in range(m):
    dpn = [0] * 27
    for j in range(27):
        dpj = dp[j]
        if i < n and j == used:
            u = 0
            for l in range(s[i]):
                if seen[l]:
                    u += 1
            dpn[j] += u
            if j+1 <= 26:
                dpn[j+1] += s[i] - u
            if seen[s[i]]:
                dpn[j] += 1
            else:
                dpn[j+1] += 1
            dpj -= 1
        if i == n and j == used:
            dpj -= 1
        dpn[j] += dpj * j
        if j + 1 <= 26:
            dpn[j+1] += dpj * (26 - j)
    for j in range(27):
        dpn[j] %= 998244353
    dp = dpn
    if i < n and not seen[s[i]]:
        used += 1
        seen[s[i]] = True
    for j in range(k, 27):
        ans += dp[j]
    ans %= 998244353

if used >= k:
    ans -= 1
print(ans % 998244353)