#include <bits/stdc++.h>
#include <atcoder/all>
using namespace std;
using mint = atcoder::modint998244353;

int main(){
    ios::sync_with_stdio(false);
    cin.tie(0);
    int n, m, k;
    string s;
    cin >> n >> m >> k >> s;
    int S = 0;
    mint ans;
    array<mint, 27> dp;
    for(int i = 0; i < m; i++){
        dp[26] *= 26;
        for(int j = 25; j >= 1; j--){
            dp[j + 1] += (26 - j) * dp[j];
            dp[j] *= j;
        }
        if(i < n){
            const int d = s[i] - 'a';
            for(int j = 0; j < d; j++){
                dp[__builtin_popcount(S | (1 << j))]++;
            }
            S |= 1 << d;
            if(i + 1 < n && __builtin_popcount(S) >= k) ans++;
        }
        ans += accumulate(dp.begin() + k, dp.end(), mint(0));
    }
    cout << ans.val() << '\n';
}