n = int(input())
s = input()
dp = [[[0,0] for _ in range(2)]for _ in range(n+1)]
dp[0][0][0] = 1
mod = 998244353
for i in range(n):
	dp[i+1][1][1] = dp[i][1][1]*25
	dp[i+1][0][1] = dp[i][0][1]*25
	dp[i+1][1][1] += dp[i][0][1]
	d = ord(s[i])-ord('a')-1
	dp[i+1][1][1] += dp[i][1][0]*max(0,d)
	dp[i+1][0][1] += dp[i][0][0]*max(0,d)
	if s[i]=='a':
		dp[i+1][1][0] += dp[i][0][0]
	else:
		dp[i+1][0][0] += dp[i][0][0]
		dp[i+1][1][0] += dp[i][1][0]
		dp[i+1][1][1] += dp[i][0][0]
	for j in range(2):
		for k in range(2):
			dp[i+1][j][k] %= mod
print(dp[n][1][1])