#line 1 "000.cpp"
#include <bits/stdc++.h>
using namespace std::literals::string_literals;
using i64 = std::int_fast64_t;
using std::cout;
using std::cerr;
using std::endl;
using std::cin;

#if defined(DONLINE_JUDGE)
	#define NDEBUG
#elif defined(ONLINE_JUDGE)
	#define NDEBUG
#endif

template<typename T> std::vector<T> make_v(size_t a){return std::vector<T>(a);}
template<typename T, typename... Ts> auto make_v(size_t a, Ts... ts){
  return std::vector<decltype(make_v<T>(ts...))>(a, make_v<T>(ts...));
}

#line 1 "/home/ecasdqina/cpcpp/libs/library_cpp/math/modint.hpp"



#line 5 "/home/ecasdqina/cpcpp/libs/library_cpp/math/modint.hpp"

namespace cplib {
template <std::uint_fast64_t Modulus>
class modint {
	using u32 = std::uint_fast32_t;
	using u64 = std::uint_fast64_t;
	using i32 = std::int_fast32_t;
	using i64 = std::int_fast64_t;

	inline u64 apply(i64 x) { return (x < 0 ? x + Modulus : x); };

public:
	u64 a;
	static constexpr u64 mod = Modulus;

	constexpr modint(const i64& x = 0) noexcept: a(apply(x % (i64)Modulus)) {}

	constexpr modint operator+(const modint& rhs) const noexcept { return modint(*this) += rhs; }
	constexpr modint operator-(const modint& rhs) const noexcept { return modint(*this) -= rhs; }
	constexpr modint operator*(const modint& rhs) const noexcept { return modint(*this) *= rhs; }
	constexpr modint operator/(const modint& rhs) const noexcept { return modint(*this) /= rhs; }
	constexpr modint operator^(const u64& k) const noexcept { return modint(*this) ^= k; }
	constexpr modint operator^(const modint& k) const noexcept { return modint(*this) ^= k.value(); }
	constexpr modint operator-() const noexcept { return modint(Modulus - a); }
	constexpr modint operator++() noexcept { return (*this) = modint(*this) + 1; }
	constexpr modint operator--() noexcept { return (*this) = modint(*this) - 1; }
	const bool operator==(const modint& rhs) const noexcept { return a == rhs.a; };
	const bool operator!=(const modint& rhs) const noexcept { return a != rhs.a; };
	const bool operator<=(const modint& rhs) const noexcept { return a <= rhs.a; };
	const bool operator>=(const modint& rhs) const noexcept { return a >= rhs.a; };
	const bool operator<(const modint& rhs) const noexcept { return a < rhs.a; };
	const bool operator>(const modint& rhs) const noexcept { return a > rhs.a; };
	constexpr modint& operator+=(const modint& rhs) noexcept {
		a += rhs.a;
		if (a >= Modulus) a -= Modulus;
		return *this;
	}
	constexpr modint& operator-=(const modint& rhs) noexcept {
		if (a < rhs.a) a += Modulus;
		a -= rhs.a;
		return *this;
	}
	constexpr modint& operator*=(const modint& rhs) noexcept {
		a = a * rhs.a % Modulus;
		return *this;
	}
	constexpr modint& operator/=(modint rhs) noexcept {
		u64 exp = Modulus - 2;
		while (exp) {
			if (exp % 2) (*this) *= rhs;

			rhs *= rhs;
			exp /= 2;
		}
		return *this;
	}
	constexpr modint& operator^=(u64 k) noexcept {
		auto b = modint(1);
		while(k) {
			if(k & 1) b = b * (*this);
			(*this) *= (*this);
			k >>= 1;
		}
		return (*this) = b;
	}
	constexpr modint& operator=(const modint& rhs) noexcept {
		a = rhs.a;
		return (*this);
	}

	const modint inverse() const {
		return modint(1) / *this;
	}
	const modint power(i64 k) const {
		if(k < 0) return modint(*this).inverse() ^ (-k);
		return modint(*this) ^ k;
	}

	explicit operator bool() const { return a; }
	explicit operator u64() const { return a; }
	constexpr u64& value() noexcept { return a; }
	constexpr const u64& value() const noexcept { return a; }

	friend std::ostream& operator<<(std::ostream& os, const modint& p) {
		return os << p.a;
	}
	friend std::istream& operator>>(std::istream& is, modint& p) {
		u64 t;
		is >> t;
		p = modint(t);
		return is;
	}
};
}


#line 21 "000.cpp"
using mint = cplib::modint<998244353>;

int main() {
	int n, m, k; scanf("%d%d%d", &n, &m, &k);
	std::string s; std::cin >> s;

	constexpr int sigma = 26;

	if (n < m) s.resize(m, 'a');

	mint ans = 0;
	int count = 0;
	std::vector<int> used(sigma);
	std::vector<mint> dp(sigma + 1);
	for (int i = 0; i < m; ++i) {
		const int ord = s[i] - 'a';

		std::vector<mint> nx(dp.size());

		for (int j = 0; j <= sigma; ++j) nx[j] += dp[j] * j;
		for (int j = 0; j < sigma; ++j) nx[j + 1] += dp[j] * (sigma - j);

		// new
		for (int j = 0; j < ord; ++j) {
			const int nc = (used[j] ? count : count + 1);

			nx[nc] += 1;
		}

		nx.swap(dp);

		if (!used[ord]) {
			++used[ord];
			++count;
		}

		if (count >= k and i < n - 1) ++ans;
		ans += std::accumulate(dp.begin() + k, dp.end(), mint(0));
	}

	printf("%lld\n", ans.value());
	return 0;
}