import sys
#input = sys.stdin.readline
#input = sys.stdin.buffer.readline

def main():
    n = int(input()); MOD = 998244353
    s = str(input())

    #dp[i][j][k]:i文字目まで見て、j=0(余裕)/1(ちょうど一致)k=0(未使用)1(a一回),
    dp = [[0]*2 for _ in range(2)]
    dp[1][0] = 1

    for i in range(n):
        p = [[0]*2 for _ in range(2)]
        p,dp = dp,p
        if s[i] != 'a':
            miman = ord(s[i]) - ord('a') #必ず1以上
            dp[0][0] = p[0][0]*25 + p[1][0]*(miman - 1)
            dp[0][1] = p[0][0]*1 + p[0][1]*25 + p[1][0] + p[1][1]*(miman - 1)
            dp[1][0] = p[1][0]
            dp[1][1] = p[1][1]
        else:
            dp[0][0] = p[0][0]*25
            dp[0][1] = p[0][0]*1 + p[0][1]*25
            dp[1][0] = 0
            dp[1][1] = p[1][0]
        #MOD取る
        for j in range(2):
            for k in range(2):
                dp[j][k] %= MOD
        #print(dp)
    ans = dp[0][1]
    print(ans%MOD)



if __name__ == '__main__':
    main()