#include <bits/stdc++.h>

using namespace std;
using ll = long long;
#define rep(i, n) for(ll i = 0, i##_len = ll(n); i < i##_len; ++i) // 0 から n-1 まで昇順

int main() {
    int n,m,k;
    cin >> n >> m >> k;
    string s;
    cin >> s;
    int bmax = 1 << 5;
    vector dp(m+1, vector(bmax, vector<ll>(2, 0)));
    dp[0][0][0] = 1;
    rep(i, m) {
        if (i < n) {
            rep(b, bmax) {
                rep(j, s[i] - 'a') {
                    int bn = b | 1 << j;
                    dp[i+1][bn][1] += dp[i][b][0];
                    dp[i+1][bn][1] %= 998244353;
                }
                int bn = b | 1 << (s[i] - 'a');
                dp[i+1][bn][0] += dp[i][b][0];
                dp[i+1][bn][0] %= 998244353;
            }
        }

        rep(b, bmax) {
            rep(j, 5) {
                int bn = b | 1 << j;
                dp[i+1][bn][1] += dp[i][b][1];
                dp[i+1][bn][1] %= 998244353;
            }
        }
    }
    ll ans = 0;
    rep(i, m+1) rep(b, bmax) rep(j, 2) {
        if (i == n && j == 0) continue;
        if (__popcount(b) >= k) ans += dp[i][b][j];
        ans %= 998244353;
    }
    cout << ans << endl;
}