#include<bits/stdc++.h>
#include<atcoder/all>
using namespace std;
using namespace atcoder;
typedef long long int ll;
typedef long double ld;
typedef vector<ll> vi;
typedef vector<vi> vvi;
typedef vector<vvi> vvvi;
typedef vector<vvvi> vvvvi;
typedef pair<ll,ll> pi;
typedef pair<ll,pi> ppi;
typedef pair<ll,ppi> pppi;
typedef pair<ll,pppi> ppppi;
#define FOR(i,l,r) for(ll i=l;i<r;i++)
#define REP(i,n) FOR(i,0,n)
#define RFOR(i,l,r) for(ll i=r-1;i>=l;i--)
#define RREP(i,n) RFOR(i,0,n)
#define ALL(x) x.begin(),x.end()
#define F first
#define S second
#define BS(A,x) binary_search(ALL(A),x)
#define LB(A,x) (ll)(lower_bound(ALL(A),x)-A.begin())
#define UB(A,x) (ll)(upper_bound(ALL(A),x)-A.begin())
#define COU(A,x) (UB(A,x)-LB(A,x))
#define sz(c) ((ll)(c).size())
/*
#include<boost/multiprecision/cpp_int.hpp>
namespace mp=boost::multiprecision;
using Bint=mp::cpp_int;
*/
template<typename T>using min_priority_queue=priority_queue<T,vector<T>,greater<T>>;
template<typename T1,typename T2>ostream&operator<<(ostream&os,pair<T1,T2>&p){os<<p.F<<" "<<p.S;return os;}
template<typename T1,typename T2>istream&operator>>(istream&is,pair<T1,T2>&p){is>>p.F>>p.S;return is;}
template<typename T>ostream&operator<<(ostream&os,vector<T>&v){REP(i,sz(v))os<<v[i]<<(i+1!=sz(v)?" ":"");return os;}
template<typename T>istream&operator>>(istream&is,vector<T>&v){for(T&in:v)is>>in;return is;}
template<class T>bool chmax(T&a,T b){if(a<b){a=b;return 1;}return 0;}
template<class T>bool chmin(T&a,T b){if(b<a){a=b;return 1;}return 0;}
ld dist(ld x1,ld y1,ld x2,ld y2){return sqrtl((x1-x2)*(x1-x2)+(y1-y2)*(y1-y2));}
//*
using mint=modint998244353;
const ll mod=998244353;
const ld EPS=1e-8;
//*/
/*
using mint=modint1000000007;
const ll mod=1000000007;
//*/
//using mint=modint;
//*
typedef vector<mint> vm;
typedef vector<vm> vvm;
typedef vector<vvm> vvvm;
typedef vector<vvvm> vvvvm;
ostream&operator<<(ostream&os,mint&a){os<<a.val();return os;}
//*/
int main(){
  ll N,M,K;string S;cin>>N>>M>>K>>S;
  vvvm DP(27,vvm(M+1));
  REP(i,27){
  	REP(j,M+1)DP[i][j].resize(28-i);
  	DP[i][0][0]=1;
  	REP(j,M)REP(k,27-i){
  		DP[i][j+1][k+1]+=DP[i][j][k]*(26-i-k);
  		DP[i][j+1][k]+=DP[i][j][k]*(i+k);
  	}
  }
  REP(j,M)REP(i,27)REP(k,28-i)DP[i][j+1][k]+=DP[i][j][k];
  vector<bool>seen(26);
  ll cnt=0;
  mint ans=0;
  REP(i,N-1){
  	if(!seen[S[i]-'a']){seen[S[i]-'a']=1;cnt++;}
  	if(cnt>=K)ans++;
  }
  REP(i,26)seen[i]=0;
  cnt=0;
  REP(i,N){
  	REP(j,S[i]-'a'){
  		ll c=cnt;
  		if(!seen[j])c++;
  		ll L=M-i-1;
  		ll t=max(0LL,K-c);
  		//0文字~L文字で新たにt種類以上
  		FOR(k,t,27-c)ans+=DP[c][L][k];
  		//cout<<i<<" "<<(char)('a'+j)<<" "<<c<<" "<<ans<<endl;
  	}
  	if(!seen[S[i]-'a']){seen[S[i]-'a']=1;cnt++;}
  }
  cout<<ans<<endl;
  return 0;
}