#include <bits/stdc++.h>
#include <atcoder/all>
using namespace std;
using namespace atcoder;
typedef int64_t lint;
#define rep(i, n) for(int i=0; i<n; i++)
#define repx(i, l, n) for(int i=l; i<n; i++)
#define all(v) v.begin(), v.end()
#define show(x) cout << #x << ": " << x << endl;
#define list(x) cout << #x << ": " << x << "  ";
#define pb push_back
using vi = vector<lint>;
using vvi = vector<vector<lint>>;
template<class T> inline void vin(vector<T>& v) { rep(i, v.size()) cin >> v.at(i); }
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; }
template<class T> inline void drop(T x) { cout << x << endl; exit(0); }
template<class T> void vout(vector<T> v) { rep(i, v.size()) { cout << v.at(i).val() << ' '; } cout << endl; }
constexpr lint LINF = LLONG_MAX/2;
using mint = modint998244353;
using vm = vector<mint>;

int main() {
	lint N, M, K;
	string S;
	cin >> N >> M >> K >> S;

	lint a=0, b=0, c=0, x, y, z;
	std::vector<vm> dp(M+1, vm(27));
	set<char> s;
	mint ans = 0;
	rep(i, M) {
		rep(j, 27) {
			dp[i+1][j] += dp[i][j]*j;
			if (j != 26) dp[i+1][j+1] += dp[i][j]*(26-j);
		}
		if (i < N) {
			rep(j, 27) {
				if (char('a'+j) == S[i]) break;
				if (s.count(char('a'+j))) dp[i+1][s.size()]++;
				else dp[i+1][s.size()+1]++;
			}
			s.insert(S[i]);
			if (i != N-1 && s.size() >= K) ans++;
		}
		repx(j, K, 27) ans += dp[i+1][j];
	}
	std::cout << ans.val() << '\n';
}