#include <stdio.h>

int main () {
  int n = 0;
  int m = 0;
  int k = 0;
  char s[500001] = "";
    
  int res = 0;
  
  long long ans = 0LL;
  long long mod_num = 998244353LL;
  
  long long cnt[26] = {};
  long long work[26] = {};
  
  int flag[26] = {};
  int tmp = 0;
  
  res = scanf("%d", &n);
  res = scanf("%d", &m);
  res = scanf("%d", &k);
  res = scanf("%s", s);
  
  for (int i = 0; i < m; i++) {
    for (int j = 0; j < 26; j++) {
      work[j] += cnt[j]*((long long)(j+1));
    }
    for (int j = 0; j < 25; j++) {
      work[j+1] += cnt[j]*((long long)(25-j));
    }
    for (int j = 0; j < (int)(s[i]-'a'); j++) {
      if (flag[j] > 0) {
        work[tmp-1] += 1LL;
      } else {
        work[tmp] += 1LL;
      }
    }
    for (int j = 0; j < 26; j++) {
      cnt[j] = work[j]%mod_num;
      work[j] = 0LL;
    }
    for (int j = k-1; j < 26; j++) {
      ans += cnt[j];
    }
    if (flag[(int)(s[i]-'a')] <= 0) {
      flag[(int)(s[i]-'a')] = 1;
      tmp++;
    }
    if (tmp >= k && i < n-1) {
      ans += 1LL;
    }
  }
  
  printf("%lld\n", ans%mod_num);
  return 0;
}