#include <bits/stdc++.h>
#ifdef LOCAL
#include <debug.hpp>
#else
#define debug(...) void(0)
#endif

#include "atcoder/modint"

using namespace std;

typedef long long ll;
#define all(x) begin(x), end(x)
constexpr int INF = (1 << 30) - 1;
constexpr long long IINF = (1LL << 60) - 1;
constexpr int dx[4] = {1, 0, -1, 0}, dy[4] = {0, 1, 0, -1};

template <class T> istream& operator>>(istream& is, vector<T>& v) {
    for (auto& x : v) is >> x;
    return is;
}

template <class T> ostream& operator<<(ostream& os, const vector<T>& v) {
    auto sep = "";
    for (const auto& x : v) os << exchange(sep, " ") << x;
    return os;
}

template <class T, class U = T> bool chmin(T& x, U&& y) { return y < x and (x = forward<U>(y), true); }

template <class T, class U = T> bool chmax(T& x, U&& y) { return x < y and (x = forward<U>(y), true); }

template <class T> void mkuni(vector<T>& v) {
    sort(begin(v), end(v));
    v.erase(unique(begin(v), end(v)), end(v));
}

template <class T> int lwb(const vector<T>& v, const T& x) { return lower_bound(begin(v), end(v), x) - begin(v); }

int popcount(signed t) { return __builtin_popcount(t); }

using mint = atcoder::modint998244353;

int main() {
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    string S;
    int N, M, K;
    cin >> N >> M >> K >> S;

    int mask = 0;
    mint ans = 0;
    vector<mint> dp(27, 0), ndp(27, 0);
    for (int i = 0; i < M; i++) {
        if (i < N) {
            int x = S[i] - 'a';
            for (int j = 0; j < x; j++) {
                int nmask = mask | 1 << j, cnt = popcount(nmask);
                ndp[cnt]++;
            }
            mask |= 1 << x;
            if (i < N - 1 and popcount(mask) >= K) ans++;
        }
        for (int j = 0; j <= 26; j++) {
            mint& val = dp[j];
            if (val == 0) continue;
            ndp[j] += val * j;
            if (j + 1 <= 26) ndp[j + 1] += val * (26 - j);
            val = 0;
        }
        swap(dp, ndp);
        for (int j = K; j <= 26; j++) ans += dp[j];
    }

    cout << ans.val() << '\n';
    return 0;
}