#include <bits/stdc++.h>
#include <atcoder/all>
#define SELECTER(_1,_2,_3,SELECT,...) SELECT
#define rep1(i,n) for(int i=0;i<(int)n;++i)
#define rep2(i,a,n) for(int i=(int)a;i<(int)n;++i)
#define rep(...) SELECTER(__VA_ARGS__,rep2,rep1)(__VA_ARGS__)
#define RSELECTER(_1, _2, _3, RSELECT, ...) RSELECT
#define rrep1(i,n) for(int i=(int)n-1;i>=0;--i)
#define rrep2(i,a,n) for(int i=(int)n-1;i>=(int)a;--i)
#define rrep(...) RSELECTER(__VA_ARGS__, rrep2, rrep1)(__VA_ARGS__)
#define all(a) a.begin(),a.end()
#define rall(a) a.rbegin(),a.rend()
#define fi first
#define se second
#define PrintR LogOutput
#ifdef _DEBUG
#define Log(...) LogOutput(__VA_ARGS__)
#else
#define Log(...)
#endif
using namespace std;
using namespace atcoder;
using ll=long long;
using pii=pair<int,int>;
using pll=pair<long long,long long>;
using pdd=pair<long double,long double>;
using veci=vector<int>;
using vecpii=vector<pair<int,int>>;
using vecll=vector<long long>;
using vecpll=vector<pair<long long,long long>>;
using vecpdd=vector<pair<long double,long double>>;
using vecs=vector<string>;
using vecb=vector<bool>;
using vecd=vector<double>;
using tp=tuple<int,int,int>;
using tpll=tuple<ll,ll,ll>;
using mint=modint998244353;
using mint10=modint1000000007;
template<typename T, typename S>
istream& operator>>(istream& in, pair<T, S>& a){return in >> a.first >> a.second;}
template<typename T, typename S>
ostream& operator<<(ostream& out, const pair<T, S>& a){return out << a.first << ' ' << a.second;}
ostream& operator<<(ostream& out, const mint& a){return out << a.val();}
ostream& operator<<(ostream& out, const mint10& a){return out << a.val();}
ostream& operator<<(ostream& out, const modint& a){return out << a.val();}
template<typename T>
ostream& operator<<(ostream& out, const vector<T>& d){for(int i = 0 ; i < d.size() ; ++i) out << d[i] << ' '; return out;}
template<typename T, typename S>
pair<T, S> operator+(const pair<T, S>& a, const pair<T, S>& b){return {a.fi + b.fi, a.se + b.se};}
template<typename T, typename S>
pair<T, S> operator-(const pair<T, S>& a, const pair<T, S>& b){return {a.fi - b.fi, a.se - b.se};}
template<class T> inline bool chmax(T& a,T b){if(a<b) {a=b;return true;} return false;}
template<class T> inline bool chmin(T& a,T b){if(a>b) {a=b;return true;} return false;}

constexpr ll INF=numeric_limits<ll>::max() / 4;
constexpr ll MOD=998244353;
const int vi[] = {0, 1, 0, -1}, vj[] = {1, 0, -1, 0};

template<typename... Args>
void LogOutput(Args&&... args){
	stringstream ss;
	((ss << args << ' '), ...);
	cout << ss.str().substr(0, ss.str().length() - 1) << endl;
}
template<typename T>
void LogOutput(vector<vector<T>>& data){for(auto d : data) LogOutput(d);}

int main(){
	ios::sync_with_stdio(false);
	std::cin.tie(nullptr);
	int n, m, k;cin>>n>>m>>k;
	string s;cin>>s;
	vector dp(m + 1, vector<mint>(28, 0));
	set<char> st;
	dp[1][1] += s[0] - 'a';
	st.insert(s[0]);
	mint ans = 0;
	rep(i, 1, m){
		int u = st.size();
		if(u >= k && i < n) ans++;
		int t = 0, t2 = 0;
		if(i < n){
			rep(j, s[i] - 'a'){
				if(st.count(j + 'a')) t++;
				else t2++;
			}
		}
		rep(j, 27){
			if(u == j) dp[i + 1][j] += t, dp[i + 1][j + 1] += t2;
			dp[i + 1][j] += dp[i][j] * j;
			dp[i + 1][j + 1] += dp[i][j] * (26 - j);
		}
		if(i < n) st.insert(s[i]);
	}
	rep(i, m + 1) rep(j, k, 27) ans += dp[i][j];
	cout<<ans<<endl;
}