#include<bits/stdc++.h>
namespace {
#pragma GCC diagnostic ignored "-Wunused-function"
#include<atcoder/all>
#pragma GCC diagnostic warning "-Wunused-function"
using namespace std;
using namespace atcoder;
#define rep(i,n) for(int i = 0; i < (int)(n); i++)
#define rrep(i,n) for(int i = (int)(n) - 1; i >= 0; i--)
#define all(x) begin(x), end(x)
#define rall(x) rbegin(x), rend(x)
template<class T> bool chmax(T& a, const T& b) { if (a < b) { a = b; return true; } else return false; }
template<class T> bool chmin(T& a, const T& b) { if (b < a) { a = b; return true; } else return false; }
using ll = long long;
using P = pair<int,int>;
using VI = vector<int>;
using VVI = vector<VI>;
using VL = vector<ll>;
using VVL = vector<VL>;
using mint = modint998244353;

constexpr int FACT_SIZE = 1000000;
mint Fact[FACT_SIZE + 1];
mint iFact[FACT_SIZE + 1];
const auto fact_init = [] {
    Fact[0] = mint::raw(1);
    for(int i = 1; i <= FACT_SIZE; ++i) {
        Fact[i] = Fact[i-1] * i;
    }
    iFact[FACT_SIZE] = Fact[FACT_SIZE].inv();
    for(int i = FACT_SIZE; i; --i) {
        iFact[i-1] = iFact[i] * i;
    }
    return false;
}();

mint comb(int n, int k) {
    if (k == 0) return mint::raw(1);
    assert(n >= 0 && k >= 0);
    if (k > n) return mint::raw(0);
    return Fact[n] * iFact[n - k] * iFact[k];
}

mint icomb(int n, int k) {
    return iFact[n] * Fact[n - k] * Fact[k];
}

mint fact(int n) {return Fact[n];}
mint perm(int n, int k) {
    assert(0 <= n);
    return Fact[n] * iFact[n - k];
}

} int main() {
  ios::sync_with_stdio(false);
  cin.tie(0);
  int n, m, k;
  cin >> n >> m >> k;
  string s;
  cin >> s;
  int seen = 0;
  mint ans;
  rep(i, n) {
    int pc = __builtin_popcount(seen);
    int x = s[i] - 'a';
    int c1 = __builtin_popcount(seen & ((1 << x) - 1));
    int c2 = x - c1;
    if (pc >= k) ans++;
    for(auto [s, c] : {pair(pc, c1), pair(pc + 1, c2)}) {
      mint d[27];
      int rest = m - (i + 1);
      for(int add = 0; add <= 26 - s; add++) {
        int t = s + add;
        mint z = t == 1 ? mint(rest + 1) : (1 - mint(t).pow(rest + 1)) / (1 - t);
        mint v = c * comb(26 - s, add) * z;
        rep(a, add) v -= d[a] * comb(26 - s - a, add - a);
        d[add] = v;
        if (s + add >= k) ans += v;
      }
    }
    seen |= 1 << x;
  }
  cout << ans.val() << endl;
}