// #pragma GCC target("avx2")
// #pragma GCC optimize("O3")
// #pragma GCC optimize("unroll-loops")
#include <algorithm>
#include <bitset>
#include <cassert>
#include <climits>
#include <cmath>
#include <complex>
#include <iomanip>
#include <iostream>
#include <map>
#include <queue>
#include <set>
#include <string>
#include <tuple>
#include <vector>
using namespace std;
using lg = long long;
using pii = pair<int, int>;
using pll = pair<lg, lg>;
#define TEST cerr << "TEST" << endl
#define AMARI 998244353
// #define AMARI 1000000007
#define TEMOTO ((sizeof(long double) == 16) ? false : true)
#define TIME_LIMIT 1980 * (TEMOTO ? 1 : 1000)
#define el '\n'
#define El '\n'
#define mpr make_pair

#define MULTI_TEST_CASE false
void solve(void) {
    int n,m,k;
    cin >> n >> m >> k;
    string s;
    cin >> s;
    vector<int> icutume(n);
    set<char> tst;
    for(int i = 0; i < s.size(); i++){
        tst.insert(s[i]);
        icutume[i] = tst.size();
    }
    vector<vector<lg>> smaller(m + 1,vector<lg>(27,0)),just(m + 1,vector<lg>(27,0));
    just[0][0] = 1;

    //配るDP
    vector<bool> visited(26,false);
    for(int i = 0; i < m; i++){
        //just →just
        if(i < n)just[i + 1][icutume[i]] = 1;
        for(int j = 0; j <= 26; j++){
            //smaller → smaller
            //if(i == 1 && j == 1)cerr << smaller[i][j] << el;
            smaller[i + 1][j] += smaller[i][j] * (lg)j; smaller[i + 1][j] %= AMARI;
            if(j != 26){
                smaller[i + 1][j + 1] += smaller[i][j] * (lg)(26 - j);
                smaller[i + 1][j + 1] %= AMARI;
            }

            //just → smaller
            if(!just[i][j])continue;
            
            int tc = 0,fc = 0;
            if(i >= s.size())continue;
            
            //smallerに持ってけるアルファベットが何種類あるか
            for(int k = 0; k < s[i] - 'a'; k++){
                if(visited[k])tc++;
                else fc++;
            }
            visited[s[i] - 'a'] = true;
            //if(i == 1)cerr << tc << ' ' << fc << el;
            smaller[i + 1][j] += tc;
            if(smaller[i + 1][j] > AMARI)smaller[i + 1][j] -= AMARI;
            if(fc){
                smaller[i + 1][j + 1] += fc;
                if(smaller[i + 1][j + 1] > AMARI)smaller[i + 1][j + 1] -= AMARI;
            }
        }
    }
    lg ans = 0;
    if(true){
        for(int i = 0; i <= m; i++){
            for(int j = 0; j <= 26; j++){
                if(j >= k)ans += smaller[i][j];
                if(ans > AMARI)ans -= AMARI;
                //cerr << smaller[i][j] << ' ';

                //if(i < n && j >= k)ans += just[i][j];
            }
            //cerr << el;
        }
        for(int i = 0; i < n - 1; i++)if(icutume[i] >= k)ans++;
        if(ans > AMARI)ans -= AMARI;
    }
    cout << ans << el;
    return;
}

void calc(void) {
    return;
}

int main(void) {
    cin.tie(nullptr);
    ios::sync_with_stdio(false);
    calc();
    int t = 1;
    if (MULTI_TEST_CASE) cin >> t;
    while (t--) {
        solve();
    }
    return 0;
}