#pragma GCC optimize("Ofast")
#pragma GCC target("avx2")
#pragma GCC optimize("O3")
#pragma GCC optimize("unroll-loops")
#include <bits/stdc++.h>
#include <algorithm>
#include <set>
#include <vector>
#include <set>
#include <queue>
#include <tuple>
#include <map>
#include <stack>
#define se second
#define fi first
using namespace std;
using ll = long long;
using ull = unsigned long long;

#define rep(i,n) for(long long i = 0; i < (int)n; i++)

#define FOR(i, m, n) for(long long i = (m);i < (n); ++i)
#define RFOR(i, n, m) for(long long i = (m-1);i >= (n); --i)
#define ALL(obj) (obj).begin(),(obj).end()
#define SPEED cin.tie(0);ios::sync_with_stdio(false);

template<class T> using V = vector<T>;
template<class T, class U> using P = pair<T, U>;
template<class T> using PQ = priority_queue<T>;
template<class T> using PQR = priority_queue<T,vector<T>,greater<T>>;
void print(V<int> ar) {
    for(auto x: ar)cout << x << " " ;
    cout << endl;
}


#include <algorithm>
#include <cassert>
#include <iostream>
#include <vector>

template <class S,
          S (*op)(S, S),
          S (*e)(),
          class F,
          S (*mapping)(F, S),
          F (*composition)(F, F),
          F (*id)()>
struct lazy_segtree {
  public:
    lazy_segtree() : lazy_segtree(0) {}
    lazy_segtree(int n) : lazy_segtree(std::vector<S>(n, e())) {}
    lazy_segtree(const std::vector<S>& v) : _n(int(v.size())) {
        /*
        log = internal::ceil_pow2(_n);
        size = 1 << log;
        */
        log = 0;
        size = 1;
        while (size < _n) size <<= 1, log++;

        d = std::vector<S>(2 * size, e());
        lz = std::vector<F>(size, id());
        for (int i = 0; i < _n; i++) d[size + i] = v[i];
        for (int i = size - 1; i >= 1; i--) {
            update(i);
        }
    }

    void set(int p, S x) {
        assert(0 <= p && p < _n);
        p += size;
        for (int i = log; i >= 1; i--) push(p >> i);
        d[p] = x;
        for (int i = 1; i <= log; i++) update(p >> i);
    }

    S get(int p) {
        assert(0 <= p && p < _n);
        p += size;
        for (int i = log; i >= 1; i--) push(p >> i);
        return d[p];
    }

    S prod(int l, int r) {
        assert(0 <= l && l <= r && r <= _n);
        if (l == r) return e();

        l += size;
        r += size;

        for (int i = log; i >= 1; i--) {
            if (((l >> i) << i) != l) push(l >> i);
            if (((r >> i) << i) != r) push(r >> i);
        }

        S sml = e(), smr = e();
        while (l < r) {
            if (l & 1) sml = op(sml, d[l++]);
            if (r & 1) smr = op(d[--r], smr);
            l >>= 1;
            r >>= 1;
        }

        return op(sml, smr);
    }

    S all_prod() { return d[1]; }

    void apply(int p, F f) {
        assert(0 <= p && p < _n);
        p += size;
        for (int i = log; i >= 1; i--) push(p >> i);
        d[p] = mapping(f, d[p]);
        for (int i = 1; i <= log; i++) update(p >> i);
    }
    void apply(int l, int r, F f) {
        assert(0 <= l && l <= r && r <= _n);
        if (l == r) return;

        l += size;
        r += size;

        for (int i = log; i >= 1; i--) {
            if (((l >> i) << i) != l) push(l >> i);
            if (((r >> i) << i) != r) push((r - 1) >> i);
        }

        {
            int l2 = l, r2 = r;
            while (l < r) {
                if (l & 1) all_apply(l++, f);
                if (r & 1) all_apply(--r, f);
                l >>= 1;
                r >>= 1;
            }
            l = l2;
            r = r2;
        }

        for (int i = 1; i <= log; i++) {
            if (((l >> i) << i) != l) update(l >> i);
            if (((r >> i) << i) != r) update((r - 1) >> i);
        }
    }

    template <bool (*g)(S)> int max_right(int l) {
        return max_right(l, [](S x) { return g(x); });
    }
    template <class G> int max_right(int l, G g) {
        assert(0 <= l && l <= _n);
        assert(g(e()));
        if (l == _n) return _n;
        l += size;
        for (int i = log; i >= 1; i--) push(l >> i);
        S sm = e();
        do {
            while (l % 2 == 0) l >>= 1;
            if (!g(op(sm, d[l]))) {
                while (l < size) {
                    push(l);
                    l = (2 * l);
                    if (g(op(sm, d[l]))) {
                        sm = op(sm, d[l]);
                        l++;
                    }
                }
                return l - size;
            }
            sm = op(sm, d[l]);
            l++;
        } while ((l & -l) != l);
        return _n;
    }

    template <bool (*g)(S)> int min_left(int r) {
        return min_left(r, [](S x) { return g(x); });
    }
    template <class G> int min_left(int r, G g) {
        assert(0 <= r && r <= _n);
        assert(g(e()));
        if (r == 0) return 0;
        r += size;
        for (int i = log; i >= 1; i--) push((r - 1) >> i);
        S sm = e();
        do {
            r--;
            while (r > 1 && (r % 2)) r >>= 1;
            if (!g(op(d[r], sm))) {
                while (r < size) {
                    push(r);
                    r = (2 * r + 1);
                    if (g(op(d[r], sm))) {
                        sm = op(d[r], sm);
                        r--;
                    }
                }
                return r + 1 - size;
            }
            sm = op(d[r], sm);
        } while ((r & -r) != r);
        return 0;
    }

  private:
    int _n, size, log;
    std::vector<S> d;
    std::vector<F> lz;

    void update(int k) { d[k] = op(d[2 * k], d[2 * k + 1]); }
    void all_apply(int k, F f) {
        d[k] = mapping(f, d[k]);
        if (k < size) lz[k] = composition(f, lz[k]);
    }
    void push(int k) {
        all_apply(2 * k, lz[k]);
        all_apply(2 * k + 1, lz[k]);
        lz[k] = id();
    }
};

using namespace std;

int op(int a, int b){return max(a,b);}
int e(){return 0;}

int mapping(int f, int x){
    if (f == -1) return x;
    return f;
}

int composition(int f, int g){
    if (f == -1) return g;
    return f;
}

int id(){return -1;}

V<V<int>> G, RG;
V<ll> df1,df2,dg1,dg2;
ll f1(int x) {
    if(df1[x]!=-1) {
        return df1[x];
    }
    ll r = 0;
    for(int y:RG[x]) {
        r+=f1(y);
    }
    df1[x] = r;
    return df1[x];
}
ll f2(int x) {
    if(df2[x]!=-1) {
        return df2[x];
    }
    ll r = 0;
    for(int y:G[x]) {
        r+=f2(y);
    }
    df2[x] = r;
    return df2[x];
}
ll g1(int x) {
    if(dg1[x]!=-1) {
        return dg1[x];
    }
    ll r = 0;
    for(int y:RG[x]) {
        r+=f1(y)+g1(y);
    }
    dg1[x] = r;
    return dg1[x];
}
ll g2(int x) {
    if(dg2[x]!=-1) {
        return dg2[x];
    }
    ll r = 0;
    for(int y:G[x]) {
        r+=f2(y)+g2(y);
    }
    dg2[x] = r;
    return dg2[x];
}

int main(){
    int n;cin >> n;
    string s;cin >> s;
    const int m = 26;
    V<int> S(n);rep(i, n)S[i] = s[i]-'a';
    const ll mod = 998244353;
    V<V<V<ll>>> dp(n+1,V<V<ll>>(2, V<ll>(2, 0)));
    dp[0][0][0] = 1;
    rep(i, n)rep(j, 2)rep(k, 2)rep(l, m) {
        int now = dp[i][j][k];
        int ni = i+1, nj = j, nk = k;
        if(j==0 && l > S[i])continue;
        if(j==0 && l < S[i])nj = 1;
        if(l == 0)nk += 1;
        if(nk==2)continue;

        dp[ni][nj][nk] += now;
        if(dp[ni][nj][nk] >= mod)dp[ni][nj][nk]-=mod;
    }
    cout << (dp[n][1][1])%mod << endl;
    
}