#include <iostream>
#include <set>
#include <vector>
using namespace std;
#define FOR(i, begin, end) for(int i=(begin),i##_end_=(end);i<i##_end_;i++)
#define IFOR(i, begin, end) for(int i=(end)-1,i##_begin_=(begin);i>=i##_begin_;i--)
#define REP(i, n) FOR(i,0,n)
#define IREP(i, n) IFOR(i,0,n)

#include <atcoder/modint>
using mint = atcoder::modint998244353;

int main() {
    int N, M, K;
    string S;
    cin >> N >> M >> K >> S;

    constexpr int D = 26;

    vector<mint> dp(D + 1);

    set<char> se;

    mint ret = 0;

    REP(i, M) {
        IREP(d, D + 1) {
            if (d + 1 <= D) dp.at(d + 1) += dp.at(d) * (D - d);
            dp.at(d) *= d;
        }

        if (i < N) {
            const int ci = S.at(i) - 'a';
            const int cnt = se.size();
            REP(d, ci) {
                dp.at(cnt + !se.count('a' + d)) += 1;
            }
        }

        if (i < N) se.insert(S.at(i));

        FOR(k, K, D + 1) ret += dp.at(k);

        if (i + 1 < N and (int)se.size() >= K) ret += 1;
    }

    cout << ret.val() << '\n';
}