// line 1 "answer.cpp"
#include <bits/stdc++.h>
#include <atcoder/modint.hpp>
using namespace std;
using mint = atcoder::modint998244353;

int main() {
    int n, m, k;
    string s;
    cin >> n >> m >> k >> s;
    vector dp(m+1, vector<mint>(27, 0));
    vector<bool> seen(26, 0);
    int used = 0;
    dp[0][0] = 1;
    for (int i=0; i<m; i++) {
        for (int j=0; j<=26; j++) {
            mint dpi = dp[i][j];
            if (i < n && j == used) {
                int u = 0;
                for(int l=0; l < s[i] - 'a'; l++) {
                    if (seen[l]) u++;
                }
                dp[i+1][j] += u;
                if (j+1 <= 26) dp[i+1][j+1] += (s[i] - 'a' - u);
                if (seen[s[i] - 'a']) dp[i+1][j] += 1;
                else dp[i+1][j+1] += 1;
                dpi -= 1;
            }
            if (i == n && j == used) dpi -= 1;
            dp[i+1][j] += dpi * j;
            if (j+1 <= 26) dp[i+1][j+1] += dpi * (26 - j);
        }
        if (i < n && !seen[s[i] - 'a']) {
            used++;
            seen[s[i] - 'a'] = true;
        }
    }
    mint ans = 0;
    for (int i=1; i<=m; i++) for (int j=k; j<=26; j++) ans += dp[i][j];
    cout << (ans-1).val() << '\n';
}