#include<atcoder/all>
#include <iostream> // cout, endl, cin
#include <string> // string, to_string, stoi
#include <vector> // vector
#include <algorithm> // min, max, swap, sort, reverse, lower_bound, upper_bound
#include <utility> // pair, make_pair
#include <tuple> // tuple, make_tuple
#include <cstdint> // int64_t, int*_t
#include <cstdio> // printf
#include <map> // map
#include <queue> // queue, priority_queue
#include <set> // set
#include <stack> // stack
#include <deque> // deque #include <unordered_map> // unordered_map #include <unordered_set> // unordered_set #include <bitset> // bitset
#include <cctype> // isupper, islower, isdigit, toupper, tolower
#include <math.h>
#include <iomanip>
#include <functional>
#include<unordered_map>
#include <random>
using namespace std;  
using namespace atcoder;
#define rep(i, n) for (int i = 0; i < (int)(n); i++)
#define repi(i, a, b) for (int i = (int)(a); i < (int)(b); i++)
#define rep2(i, m, n) for (int i = (m); i < (n); ++i)
#define drep2(i, m, n) for (int i = (m)-1; i >= (n); --i)
#define drep(i, n) drep2(i, n, 0)
//#define endl '\n'
#define all(x) (x).begin(),(x).end()
#define arr(x) (x).rbegin(),(x).rend()
typedef long long ll;
typedef unsigned long long ull;
const ll inf=1e18;  
//const int inf=1e7;  
using graph = vector<vector<int> > ;
using P= pair<ll,ll>;  
using vi=vector<int>;
using vvi=vector<vi>;
using vll=vector<ll>; 
using vvll=vector<vll>;
using vp=vector<P>;
using vvp=vector<vp>;
using vd=vector<double>;
using vvd =vector<vd>;
//string T="ABCDEFGHIJKLMNOPQRSTUVWXYZ";
//string S="abcdefghijklmnopqrstuvwxyz";
//g++ main.cpp -std=c++17 -I .  
//cout <<setprecision(20);
//cout << fixed << setprecision(10);
//cin.tie(0); ios::sync_with_stdio(false);

const double PI = acos(-1);
int vx[]={0,1,0,-1,-1,1,1,-1},vy[]={1,0,-1,0,1,1,-1,-1};
void putsYes(bool f){cout << (f?"Yes":"No") << endl;}
void putsYES(bool f){cout << (f?"YES":"NO") << endl;}
void putsFirst(bool f){cout << (f?"First":"Second") << endl;}
void debug(int test){cout << "TEST" << " " << test << endl;}
ll pow_pow(ll x,ll n,ll mod){
    if(n==0) return 1; 
    x%=mod;
    ll res=pow_pow(x*x%mod,n/2,mod);
    if(n&1)res=res*x%mod;
    return res;
}
ll gcdll(ll x,ll y){
    if(y==0)return x;
    return gcdll(y,x%y);
}
//ll INFF=1000100100100100100;
ll lcmll(ll x,ll y){
    ll X=(x/gcdll(x,y)),Y=y;
    return X*Y;
}
template<class T> bool chmin(T& a, T b) {
    if (a > b) {
        a = b;
        return true;
    }
    else return false;
}
template<class T> bool chmax(T& a, T b) {
    if (a < b) {
        a = b;
        return true;
    }
    else return false;
}
struct edge{
  int to; ll cost;
  edge(int to,ll cost) : to(to),cost(cost){}
};
using ve=vector<edge>;
using vve=vector<ve>;
using mint = modint998244353;
using vm=vector<mint>;
using vvm=vector<vm>;
const int mod = 998244353;
//int mod = 1e9+7;
constexpr ll MAX = 30;
ll fact[MAX],finv[MAX],inv[MAX];
void initcomb(){
  fact[0]=fact[1]=1;
  finv[0]=finv[1]=1;
  inv[1]=1;
  for(int i=2;i<MAX;i++){
    fact[i]=fact[i-1]*i%mod;
    inv[i]=mod-inv[mod%i]*(mod/i)%mod;
    finv[i]=finv[i-1]*inv[i]%mod;
  }
}
ll comb(ll n,ll k){
  if(n<k) return 0;
  if(n<0||k<0) return 0;
  return fact[n]*(finv[k]*finv[n-k]%mod)%mod;
}
vll anss;
mint dp[27][500005][27];
void solve(int test){
  int n,m,k; cin >> n >> m >> k;
  string s; cin >> s;
  vi seen(26);
  int num=0;
  mint ans=0;
  vm pow26(m+1,1);
  repi(i,1,m+1)pow26[i]=pow26[i-1]*26;
  repi(i,1,m+1)pow26[i]+=pow26[i-1];
  rep(k,27)rep(i,m+1)rep(j,27)dp[k][i][j]=0;
  rep(k,27)dp[k][0][0]=1;
  rep(k,27)rep(i,m)rep(j,27){
    if(dp[k][i][j].val()==0)continue;
    dp[k][i+1][j]+=dp[k][i][j]*(k+j);
   if(j+1<=26 &&  26-(k+j)>=0)dp[k][i+1][j+1]+=dp[k][i][j]*(26-(k+j));
  }
  rep(k,27){
    rep(i,m+1)repi(j,1,27)dp[k][i][j]+=dp[k][i][j-1];
    rep(j,27)repi(i,1,m+1)dp[k][i][j]+=dp[k][i-1][j];
  }
  {
    rep(j,26)if((s[0]-'a')>j){
      int nownum=1;
      mint now=pow26[m-1-(0)];
      if(nownum>=k)ans+=now;
      else {
        int d=k-1-nownum;
        now-=dp[nownum][m-1-(0)][d];
        ans+=now;
      }
    }
  }
  rep(i,n-1){
    if(seen[s[i]-'a']==0)num++;
    seen[s[i]-'a']=1;
    if(num>=k)ans++;
    rep(j,26)if((s[i+1]-'a')>j){
      int nownum=num+(seen[j]==0);
      mint now=pow26[m-1-(i+1)];
      if(nownum>=k)ans+=now;
      else {
        int d=k-1-nownum;
        now-=dp[nownum][m-1-(i+1)][d];
        ans+=now;
      }
    }
  }
  cout << ans.val() <<  endl;
}
//g++ main.cpp -std=c++17 -I .
int main(){cin.tie(0);ios::sync_with_stdio(false);
 int t=1;//cin >>t;
 rep(test,t)solve(test);
 for(auto ans:anss)cout << ans << endl;
}