#include #include using namespace std; using namespace atcoder; //using mint = modint1000000007; //const int mod = 1000000007; using mint = modint998244353; const int mod = 998244353; //const int INF = 1e9; //const long long LINF = 1e18; #define rep(i, n) for (int i = 0; i < (n); ++i) #define rep2(i,l,r)for(int i=(l);i<(r);++i) #define rrep(i, n) for (int i = (n-1); i >= 0; --i) #define rrep2(i,l,r)for(int i=(r-1);i>=(l);--i) #define all(x) (x).begin(),(x).end() #define allR(x) (x).rbegin(),(x).rend() #define endl "\n" #define P pair template inline bool chmax(A & a, const B & b) { if (a < b) { a = b; return true; } return false; } template inline bool chmin(A & a, const B & b) { if (a > b) { a = b; return true; } return false; } struct combination { vector fact, ifact; combination(int n) :fact(n + 1), ifact(n + 1) { assert(n < mod); fact[0] = 1; for (int i = 1; i <= n; ++i) fact[i] = fact[i - 1] * i; ifact[n] = fact[n].inv(); for (int i = n; i >= 1; --i) ifact[i - 1] = ifact[i] * i; } mint operator()(int n, int k) { return com(n, k); } mint com(int n, int k) { //負の二項係数を考慮する場合にコメントアウトを外す //if (n < 0) return com(-n, k) * (k % 2 ? -1 : 1); if (k < 0 || k > n) return 0; return fact[n] * ifact[k] * ifact[n - k]; } mint comsub(long long n, long long k) { if (n - k < k) k = n - k; assert(k < (int)fact.size()); mint val = ifact[k]; rep(i, k) val *= n - i; return val; } mint div(int x) { if (x >= (int)fact.size())return mint(x).inv(); return fact[x - 1] * ifact[x]; } mint inv(int n, int k) { //if (n < 0) return inv(-n, k) * (k % 2 ? -1 : 1); if (k < 0 || k > n) return 0; return ifact[n] * fact[k] * fact[n - k]; } mint p(int n, int k) { return fact[n] * ifact[n - k]; } }c(2000006); mint solve(int sz, int x, int k) { // 長さsz以下、x種類はすでに使っている、k種類は最低必要 vector dp(27);//new col mint ret = 0; rep(i, 27) { mint val = 0; if (1 == i + x) { val = sz + 1; } else { val = (mint)(pow_mod(i + x, sz + 1, mod) - 1); val /= i + x - 1; } dp[i] = val; rep(j, i)dp[i] -= dp[j] * c(i, j); } rep(i, 27) { if (i + x > 26)continue; if (i + x < k)continue; ret += dp[i] * c(26 - x, i); } return ret; } int main() { ios::sync_with_stdio(false); cin.tie(nullptr); int n, m, k; cin >> n >> m >> k; string s; cin >> s; vectorchk(26); int cnt = 0; mint ans = 0; rep(i, s.size()) { if (cnt >= k)ans++; int x = s[i] - 'a'; int c0 = 0, c1 = 0; rep(j, x) { if (!chk[j])c1++; else c0++; } int sz = m - (i + 1); ans += solve(sz, cnt, k)*c0; ans += solve(sz, cnt + 1, k)*c1; if (!chk[s[i] - 'a']) { chk[s[i] - 'a'] = true; cnt++; } } cout << ans.val() << endl; return 0; }