#include <iostream>
#include <algorithm>
#include <iomanip>
#include <vector>
#include <queue>
#include <deque>
#include <set>
#include <map>
#include <tuple>
#include <cmath>
#include <numeric>
#include <functional>
#include <cassert>
#include <atcoder/modint>

#define debug_value(x) cerr << "line" << __LINE__ << ":<" << __func__ << ">:" << #x << "=" << x << endl;
#define debug(x) cerr << "line" << __LINE__ << ":<" << __func__ << ">:" << x << endl;

template<class T> inline bool chmax(T& a, T b) { if (a < b) { a = b; return 1; } return 0; }
template<class T> inline bool chmin(T& a, T b) { if (a > b) { a = b; return 1; } return 0; }

using namespace std;
typedef long long ll;

template<typename T>
vector<vector<T>> vec2d(int n, int m, T v){
    return vector<vector<T>>(n, vector<T>(m, v));
}

template<typename T>
vector<vector<vector<T>>> vec3d(int n, int m, int k, T v){
    return vector<vector<vector<T>>>(n, vector<vector<T>>(m, vector<T>(k, v)));
}

template<typename T>
void print_vector(vector<T> v, char delimiter=' '){
    if(v.empty()) {
        cout << endl;
        return;
    }
    for(int i = 0; i+1 < v.size(); i++) cout << v[i] << delimiter;
    cout << v.back() << endl;
}

using mint = atcoder::modint998244353;

ostream& operator<<(ostream& os, const mint& m){
    os << m.val();
    return os;
}

#define N_MAX 500005
mint inv[N_MAX],fac[N_MAX],finv[N_MAX];
mint pw[27][N_MAX];

void init(){
    for(int x = 1; x <= 26; x++){
        pw[x][0] = 1;
        for(int i = 1; i < N_MAX; i++) pw[x][i] = pw[x][i-1]*x;
    }
    const ll MOD = mint::mod();
    fac[0]=1;fac[1]=1;
    finv[0]=1;finv[1]=1;
    inv[1]=1;
    for(int i=2;i<N_MAX;i++){
        inv[i]=mint(MOD)-inv[MOD%i]*(MOD/i);
        fac[i]=fac[i-1]*(ll) i;
        finv[i]=finv[i-1]*inv[i];
    }
}

mint comb(ll n, ll r){
    if(n < r){
        return mint(0);
    }else{
        return fac[n]*finv[r]*finv[n-r];
    }
}

int main(){
    ios::sync_with_stdio(false);
    cin.tie(0);
    cout << setprecision(10) << fixed;
    init();
    int n, m, k; cin >> n >> m >> k;
    string s; cin >> s;
    vector<bool> used(26);
    int cnt_used = 0;
    mint ans = 0;
    for(int i = 0; i < n && i < m; i++){
        map<int, mint> memo;
        int len = m-i-1;
        // debug_value(len)
        // x個使った
        auto solve = [&](int x){
            assert(x > 0);
            if(memo.count(x)) return memo[x];
            mint ans = (pw[26][len+1]-1)*inv[25];
            if(x >= k){
                // もう何を選んでも良い
                memo[x] = ans;
                return ans;
            }
            vector<mint> ng(k-x);
            // 追加でy個選ぶ
            for(int y = 0; y < k-x; y++){
                if(x+y == 1){
                    ng[y] = len+1;
                    continue;
                }
                mint c = (pw[x+y][len+1]-1)*inv[x+y-1];
                for(int a = 0; a < y; a++){
                    c -= comb(y, a)*ng[a];
                }
                ng[y] = c;
            }
            // print_vector(ng);
            for(int y = 0; y < k-x; y++){
                ans -= comb(26-x, y)*ng[y];
            }
            memo[x] = ans;
            return ans;
        };
        for(char c = 'a'; c < s[i]; c++){
            int x = cnt_used;
            if(!used[c-'a']) x++;
            ans += solve(x);
            // cout << x << ' ' << i << ' ' << solve(x) << endl;
        }

        if(!used[s[i]-'a']){
            cnt_used++;
            used[s[i]-'a'] = true;
        }
        if(i+1 < n && cnt_used >= k) ans++;
    }
    cout << ans << endl;
}