import java.util.Scanner;

public class Main {
	public static void main(String[] args) {
		try (Scanner sc = new Scanner(System.in)) {
			int N = sc.nextInt();
			char[] S = sc.next().toCharArray();
			final int MOD = 998_244_353;
			final int LESS = 0, EQUAL = 1;
			long[][][] dp = new long[2][2][N + 1];
			dp[EQUAL][0][0] = 1;
			for (int i = 0;i < N;++ i) {
				if (S[i] != 'a') {
					dp[EQUAL][0][i + 1] = dp[EQUAL][0][i];
					dp[EQUAL][1][i + 1] = dp[EQUAL][1][i];
				} else dp[EQUAL][1][i + 1] = dp[EQUAL][0][i];
				dp[LESS][0][i + 1] = dp[EQUAL][0][i] * Math.max(0, S[i] - 'b');
				dp[LESS][0][i + 1] += dp[LESS][0][i] * 25;
				dp[LESS][0][i + 1] %= MOD;
				if (S[i] != 'a') dp[LESS][1][i + 1] = dp[EQUAL][0][i];
				dp[LESS][1][i + 1] += dp[EQUAL][1][i] * Math.max(0, S[i] - 'b');
				dp[LESS][1][i + 1] += dp[LESS][0][i];
				dp[LESS][1][i + 1] += dp[LESS][1][i] * 25;
				dp[LESS][1][i + 1] %= MOD;
			}
			System.out.println(dp[LESS][1][N]);
		}
	}
}