#include <iostream>
#include <string>
#include <vector>
#include <algorithm>
#include <atcoder/modint>
using namespace std;
using i32 = int;
using u32 = unsigned int;
using i64 = long long;
using u64 = unsigned long long;
#define rep(i,n) for(int i=0; i<(int)(n); i++)
const i64 INF = 1001001001001001001;

using Modint = atcoder::static_modint<998244353>;


int main(){
    int N; cin >> N;
    int M; cin >> M;
    int K; cin >> K;
    string S; cin >> S;
    vector<int> F(N+1);
    rep(i,N) F[i+1] = F[i] | (1 << (S[i] - 'a'));
    Modint ans = 0;
    vector<Modint> X(28, 0);
    auto procX = [&](){
        vector<Modint> tmp(28, 0);
        rep(i,27){
            tmp[i+1] += X[i] * Modint::raw(26-i);
            tmp[i] += X[i] * Modint::raw(i);
        }
        swap(tmp, X);
    };
    for(int i=0; i<N; i++){
        procX();
        int cnt0 = 0, cnt1 = 0;
        for(int c=0; c<S[i]-'a'; c++){
            if(F[i] & (1<<c)) cnt0++; else cnt1++;
        }
        int pc = 0;
        rep(c,26) pc += (F[i] >> c) & 1;
        if(i < N && pc >= K) ans += 1;
        X[pc] += cnt0;
        X[pc+1] += cnt1;
        for(int j=K; j<=26; j++) ans += X[j];
    }
    for(int i=N; i<M; i++){
        procX();
        for(int j=K; j<=26; j++) ans += X[j];
    }
    cout << ans.val() << endl;
    return 0;
}


struct ios_do_not_sync{
    ios_do_not_sync(){
        ios::sync_with_stdio(false);
        cin.tie(nullptr);
    }
} ios_do_not_sync_instance;