pub mod io {
    pub fn scan<R: std::io::BufRead>(r: &mut R) -> Vec<u8> {
        let mut res = Vec::new();
        loop {
            let buf = match r.fill_buf() {
                Ok(buf) => buf,
                Err(e) if e.kind() == std::io::ErrorKind::Interrupted => continue,
                Err(e) => panic!("{}", e), 
            };
            let (done, used, buf) = match buf.iter().position(u8::is_ascii_whitespace) {
                Some(i) => (i > 0 || res.len() > 0, i + 1, &buf[..i]),
                None => (buf.is_empty(), buf.len(), buf),
            };
            res.extend_from_slice(buf);
            r.consume(used);
            if done { return res; }
        }
    }

    #[macro_export]
    macro_rules! scan {
        ($r:expr, [$t:tt; $n:expr]) => ((0..$n).map(|_| scan!($r, $t)).collect::<Vec<_>>());
        ($r:expr, [$t:tt]) => (scan!($r, [$t; scan!($r, usize)]));
        ($r:expr, ($($t:tt),*)) => (($(scan!($r, $t)),*));
        ($r:expr, Usize1) => (scan!($r, usize) - 1);
        ($r:expr, String) => (String::from_utf8(scan!($r, Bytes)).unwrap());
        ($r:expr, Bytes) => (io::scan($r));
        ($r:expr, $t:ty) => (scan!($r, String).parse::<$t>().unwrap());
    }

    #[macro_export]
    macro_rules! input {
        ($r:expr, $($($v:ident)* : $t:tt),* $(,)?) => {
            $(let $($v)* = scan!($r, $t);)*
        };
    }
}

const MOD: u64 = 998_244_353;

fn run<R: std::io::BufRead, W: std::io::Write>(reader: &mut R, writer: &mut W) {
    input! {
        reader,
        _n: usize,
        s: Bytes,
    }

    // inner, inner_a, border, border_a
    let mut dp = vec![0; 4];
    dp[2] = 1;
    for b in s {
        let mut ndp = vec![0; 4];
        ndp[0] += dp[0] * 25;
        ndp[1] += dp[0] + dp[1] * 25;
        if b == b'a' {
            if dp[2] == 1 {
                ndp[2] = 0;
                ndp[3] = 1;    
            } else {
                ndp[2] = 0;
                ndp[3] = 0;
            }
        } else {
            ndp[0] += dp[2] * (b - b'b') as u64;
            ndp[1] += dp[2] + dp[3] * (b - b'b') as u64;
            ndp[2] = dp[2];
            ndp[3] = dp[3];    
        }
        dp = ndp;
        dp.iter_mut().for_each(|dp| *dp %= MOD);
    }
    writeln!(writer, "{}", dp[1]).ok();
}

fn main() {
    let (stdin, stdout) = (std::io::stdin(), std::io::stdout());
    let ref mut reader = std::io::BufReader::new(stdin.lock());
    let ref mut writer = std::io::BufWriter::new(stdout.lock());
    run(reader, writer);
}