#pragma GCC optimize ("O3")
#pragma GCC target ("sse,sse2,sse3,ssse3,sse4,popcnt,abm,avx")

#include <array> // array, swap
#include <bit> // (C++20) popcount
#include <cstdlib> // abort
#include <iostream> // cin, cout, endl
#include <string> // string

#define MOD 998244353
#define KMAX 26
#define KMAX2 (KMAX+2)

using ull = unsigned long long;

int main() {
	ull n, m, k;
	std::string s;
	std::cin >> n >> m >> k >> s;
	
    if(n < 1 || n > m || m > 500000 || s.length() != n || k < 1 || k > KMAX) {
        std::abort();
    }

	ull kbits = 0, kbc = 0, result = 0;
	std::array<ull, KMAX2> dp, ndp;
	dp.fill(0);

	for(auto it = s.begin(); it != s.end(); it++) {
		ull ci = *it - 'a';
		if(ci >= KMAX) {
		    std::abort;
		}
		ndp.fill(0);
		ull same = std::popcount(kbits & ((1 << ci) - 1));
		ndp[kbc] += same;
		ndp[kbc + 1] += ci - same;
		if((kbits & (1 << ci)) == 0) {
			kbits |= (1 << ci);
			kbc += 1;
		}
		if(kbc >= k) {
			result += 1;
		}
		for(ull j = 1; j <= KMAX; j++) {
			ndp[j] += j * dp[j];
			ndp[j + 1] += (KMAX - j) * dp[j];
			ndp[j] %= MOD;
		}
		for(ull j = k; j <= KMAX; j++) {
			result += ndp[j];
		}
		dp.swap(ndp);
	}

	if(kbc >= k) {
		result -= 1;
	}

	for(ull i = n; i < m; i++) {
		ndp.fill(0);
		for(ull j = 1; j <= KMAX; j++) {
			ndp[j] += j * dp[j];
			ndp[j + 1] += (KMAX - j) * dp[j];
			ndp[j] %= MOD;
		}
		for(ull j = k; j <= KMAX; j++) {
			result += ndp[j];
		}
		dp.swap(ndp);
	}
	
	result %= MOD;
	std::cout << result << std::endl;
}