#pragma region template
#include <bits/stdc++.h>

#include <atcoder/modint.hpp>

using namespace std;
using namespace atcoder;

// clang-format off
using mint = static_modint<998244353>;
using vm = vector<mint>;
using vvm = vector<vm>;
ostream& operator<<(ostream& os, const mint& v){ os << v.val(); return os; }

using ll = long long; using vl = vector<ll>; using vvl = vector<vl>;
using ld = long double; using vld = vector<ld>; using vvld = vector<vld>;
using pll = pair<ll, ll>; using vpll = vector<pll>; using vvpll = vector<vpll>;
template <class T> using V = vector<T>; template <class T> using VV = vector<V<T>>;
template <class T> using VVV = vector<VV<T>>;
using vb = vector<bool>;
using vs = vector<string>;
using mll = map<ll, ll>;
using msl = map<string, ll>;
template<class T> using     heap = priority_queue<T>;
template<class T> using min_heap = priority_queue<T, vector<T>, greater<T>>;
constexpr ll inf = 3001001000100100100LL;
constexpr int inf_int = 1000000009;
#define endl '\n'

#define  _overload(_1, _2, _3, name, ...) name
#define   rep(...) _overload(__VA_ARGS__,   _rep,   _rep2,)(__VA_ARGS__)
#define  repc(...) _overload(__VA_ARGS__,  _repc,  _repc2,)(__VA_ARGS__)
#define  repr(...) _overload(__VA_ARGS__,  _repr,  _repr2,)(__VA_ARGS__)
#define reprc(...) _overload(__VA_ARGS__, _reprc, _reprc2,)(__VA_ARGS__)
#define   _rep(i,k,n) for(ll i=(k)  , i##_xxxx=(n); i < i##_xxxx; ++i)
#define  _repc(i,k,n) for(ll i=(k)  , i##_xxxx=(n); i <=i##_xxxx; ++i)
#define  _repr(i,k,n) for(ll i=(n)-1, i##_xxxx=(k); i >=i##_xxxx; --i)
#define _reprc(i,k,n) for(ll i=(n)  , i##_xxxx=(k); i >=i##_xxxx; --i)
#define   _rep2(i,n)   _rep(i,0,n)
#define  _repc2(i,n)  _repc(i,1,n)
#define  _repr2(i,n)  _repr(i,0,n)
#define _reprc2(i,n) _reprc(i,1,n)

#define rall(o) rbegin(o), rend(o)
#define  all(o)  begin(o),  end(o)
template <class C> ll sz(const C& c) { return static_cast<ll>(c.size()); }
template <class T> bool chmax(T& m, const T& v){ if (m < v){ m = v; return true; } return false; }
template <class T> bool chmin(T& m, const T& v){ if (v < m){ m = v; return true; } return false; }
template <class T> T udiv(const T& a, const T& b){ return (a + b - 1) / b; }
template <class T> T rdiv(const T& a, const T& b){ return (a + b / 2) / b; }
template <class T, class S>             string join(const T& v, const S& sep                  ){ stringstream ss; bool f = false; for (const auto& e : v){ if (f) ss << sep; f = true; ss << e;} return ss.str(); }
template <class T, class S, class... U> string join(const T& v, const S& sep, const U& ...args){ stringstream ss; bool f = false; for (const auto& c : v){ if (f) ss << sep; f = true; ss << join(c, args...); } return ss.str(); }
template <class T>            ostream& operator<<(ostream& os, const vector<T>&            seq){ os << '[' << join(seq, ",") << ']'; return os; } template <class T>            ostream& operator<<(ostream& os, const vector<vector<T>>&    seq){ os << '[' << join(seq, ",\n ") << ']'; return os; }
template <class T>            ostream& operator<<(ostream& os, const deque<T>&             seq){ os << '[' << join(seq, ",") << ']'; return os; }
template <class T>            ostream& operator<<(ostream& os, const set<T>&               seq){ os << '{' << join(seq, ",") << '}'; return os; }
template <class T , class TH> ostream& operator<<(ostream& os, const unordered_set<T, TH>& seq){ os << '{' << join(seq, ",") << '}'; return os; }
template <class TK, class TV> ostream& operator<<(ostream& os, const map<TK, TV>&          seq){ os << '{'; bool f = false; for (const auto& e : seq){ if (f) os << ','; f = true; os << e.first << ":" << e.second; } os << '}'; return os; }
template <class T1, class T2> ostream& operator<<(ostream& os, const pair<T1, T2>&          pa){ os << '(' << pa.first << ',' << pa.second << ')'; return os; }

#if LOCAL
#define debug(...) _debug(__VA_ARGS__, __LINE__)
#else
#define debug(...)
#endif
void print() { std::cout << '\n'; }
template <class S>             void  print(const S& a){ std::cout << a << '\n'; }
template <class S>             void _debug(const S& a){ std::cerr << "(L:" << std::setw(3) << a << ")\n"; }
template <class S, class... T> void  print(const S& a, const T&... args){ std::cout << a << ' ';  print(args...); }
template <class S, class... T> void _debug(const S& a, const T&... args){ std::cerr << a << ' '; _debug(args...); }

struct setup_main { setup_main() { std::cin.tie(nullptr); std::ios::sync_with_stdio(false); std::cout << fixed << setprecision(15); } } setup_main_;
// clang-format on
#pragma endregion

/*/
桁dp

dp[i][smaller][a]

dp[i][1][1] = 上からi桁を見て、aを一つ含み、確実にSより小さいような組み合わせ
dp[i][1][0] = 上からi桁を見て、aを含まず、確実にSより小さいような組み合わせ
dp[i][0][*] = 上からi桁を見て、Sと一致する組み合わせ
/*/

void solve(ll N, string S) {
    vector<vector<vector<mint>>> dp(N + 1, vvm(2, vm(2, 0)));
    dp[0][0][0] = 1;

    rep(i, N) rep(smaller, 2) rep(a, 2) {
        debug(i, smaller, a, dp[i][smaller][a]);
        for (char x = 'a'; x <= (smaller ? 'z' : S[i]); x++) {
            if (x == 'a' and a) continue;
            dp[i + 1][smaller or x < S[i]][a or x == 'a'] += dp[i][smaller][a];
        }
    }

    debug(dp);
    print(dp[N][1][1]);
}

int main() {
    ll N;
    string S;
    cin >> N >> S;

    solve(N, S);
}