#include <iostream>
#include <string>
#include <atcoder/modint>
#define rep(i, n) for(i = 0; i < n; i++)
#define int long long
using namespace std;
using namespace atcoder;
using mint = modint998244353;

int mod = 998244353;
int n;
string s;
mint fact[500001], finv[500001], inv[500001];

mint comb(int n, int k) {
	return fact[n] * finv[k] * finv[n - k];
}

signed main() {
	int i;

	cin >> n >> s;
	
	fact[0] = fact[1] = finv[0] = finv[1] = inv[1] = 1;
	for (i = 2; i <= n; i++) {
		fact[i] = fact[i - 1] * i;
		inv[i] = -inv[mod % i] * (mod / i);
		finv[i] = finv[i - 1] * inv[i];
	}
	if (s[0] == s[1]) {
		mint ans = 0;
		rep(i, n / 2 + 1) {
			ans += comb(n / 2, i) * comb(n / 2, i);
		}
		cout << ans.val() << endl;
	}
	else {
		cout << mint(2).pow(n / 2).val() << endl;
	}
	return 0;
}