/* #region header */ #pragma GCC optimize("O3") //コンパイラ最適化用 #ifdef LOCAL #define _GLIBCXX_DEBUG //配列に[]でアクセス時のエラー表示 #endif #define _USE_MATH_DEFINES #include // CodeForcesの場合ファイルごとに入れる #include // #include // #include using namespace std; using namespace atcoder; typedef long long LL; typedef long double LD; #define ALL(x) x.begin(), x.end() const long long INF = numeric_limits::max() / 4; const int MOD = 1e9 + 7; // const int MOD=998244353; //略記 #define FF first #define SS second #define int long long #define stoi stoll #define pii pair #define PII pair #define PB push_back #define EB emplace_back #define MP make_pair #define SZ(x) (int)((x).size()) #define VB vector #define VVB vector> #define VI vector #define VVI vector> // rep macro #define FOA(v, a) for (auto &v : a) #define REPname(a, b, c, d, e, ...) e #define REP(...) REPname(__VA_ARGS__, REP3, REP2, REP1, REP0)(__VA_ARGS__) #define REP0(x) for (int i = 0; i < (x); ++i) #define REP1(i, x) for (int i = 0; i < (x); ++i) #define REP2(i, l, r) for (int i = (l); i < (r); ++i) #define REP3(i, l, r, c) for (int i = (l); i < (r); i += (c)) #define RREPname(a, b, c, d, e, ...) e #define RREP(...) RREPname(__VA_ARGS__, RREP3, RREP2, RREP1, RREP0)(__VA_ARGS__) #define RREP0(x) for (int i = (x)-1; i >= 0; --i) #define RREP1(i, x) for (int i = (x)-1; i >= 0; --i) #define RREP2(i, l, r) for (int i = (r)-1; i >= (l); --i) #define RREP3(i, l, r, c) for (int i = (r)-1; i >= (l); i -= (c)) const int dx[4] = {0, 1, 0, -1}, dy[4] = {-1, 0, 1, 0}; const int Dx[8] = {0, 1, 1, 1, 0, -1, -1, -1}, Dy[8] = {-1, -1, 0, 1, 1, 1, 0, -1}; // input macro template std::istream &operator>>(std::istream &is, std::pair &p) { is >> p.first >> p.second; return is; } template std::istream &operator>>(std::istream &is, std::vector &v) { for (T &i : v) is >> i; return is; } std::istream &operator>>(std::istream &is, __int128_t &a) { std::string s; is >> s; __int128_t ret = 0; for (int i = 0; i < s.length(); i++) if ('0' <= s[i] and s[i] <= '9') ret = 10 * ret + s[i] - '0'; a = ret * (s[0] == '-' ? -1 : 1); return is; } namespace scanner { void scan(int &a) { std::cin >> a; } // void scan(long long &a) { std::cin >> a; } void scan(std::string &a) { std::cin >> a; } void scan(char &a) { std::cin >> a; } void scan(char a[]) { std::scanf("%s", a); } void scan(double &a) { std::cin >> a; } void scan(long double &a) { std::cin >> a; } template void scan(std::pair &p) { std::cin >> p; } template void scan(std::vector &a) { std::cin >> a; } void INPUT() {} template void INPUT(Head &head, Tail &...tail) { scan(head); INPUT(tail...); } } // namespace scanner #define VEC(type, name, size) \ std::vector name(size); \ scanner::INPUT(name) #define VVEC(type, name, h, w) \ std::vector> name(h, std::vector(w)); \ scanner::INPUT(name) #define INT(...) \ int __VA_ARGS__; \ scanner::INPUT(__VA_ARGS__) #define LONL(...) \ long long __VA_ARGS__; \ scanner::INPUT(__VA_ARGS__) #define STR(...) \ std::string __VA_ARGS__; \ scanner::INPUT(__VA_ARGS__) #define CHAR(...) \ char __VA_ARGS__; \ scanner::INPUT(__VA_ARGS__) #define DOUBLE(...) \ double __VA_ARGS__; \ scanner::INPUT(__VA_ARGS__) #define LOND(...) \ long double __VA_ARGS__; \ scanner::INPUT(__VA_ARGS__) int in() { int x; cin >> x; return x; } // https://qiita.com/Lily0727K/items/06cb1d6da8a436369eed#c%E3%81%A7%E3%81%AE%E5%AE%9F%E8%A3%85 void print() { cout << "\n"; } template void print(Head &&head, Tail &&...tail) { cout << head; if (sizeof...(tail) != 0) cout << " "; print(forward(tail)...); } template void print(vector &vec) { for (auto &a : vec) { cout << a; if (&a != &vec.back()) cout << " "; } cout << "\n"; } template void print(set &set) { for (auto &a : set) { cout << a << " "; } cout << "\n"; } template void print(vector> &df) { for (auto &vec : df) { print(vec); } } void Yes(const bool b = true) { std::cout << (b ? "Yes\n" : "No\n"); } void No() { std::cout << "No\n"; } void YES(const bool b = true) { std::cout << (b ? "YES\n" : "NO\n"); } void NO() { std::cout << "NO\n"; } // debug macro // https://atcoder.jp/contests/abc202/submissions/22815715 namespace debugger { template void view(const std::vector &a) { std::cerr << "{ "; for (const auto &v : a) { std::cerr << v << ", "; } std::cerr << "\b\b }"; } template void view(const std::vector> &a) { std::cerr << "{\n"; for (const auto &v : a) { std::cerr << "\t"; view(v); std::cerr << "\n"; } std::cerr << "}"; } template void view(const std::vector> &a) { std::cerr << "{\n"; for (const auto &p : a) std::cerr << "\t(" << p.first << ", " << p.second << ")\n"; std::cerr << "}"; } template void view(const std::map &m) { std::cerr << "{\n"; for (const auto &p : m) std::cerr << "\t[" << p.first << "] : " << p.second << "\n"; std::cerr << "}"; } template void view(const std::pair &p) { std::cerr << "(" << p.first << ", " << p.second << ")"; } template void view(const std::set &s) { std::cerr << "{ "; for (auto &v : s) { view(v); std::cerr << ", "; } std::cerr << "\b\b }"; } template void view(const T &e) { std::cerr << e; } } // namespace debugger #ifdef LOCAL void debug_out() {} template void debug_out(Head H, Tail... T) { debugger::view(H); std::cerr << ", "; debug_out(T...); } #define debug(...) \ do { \ std::cerr << __LINE__ << " [" << #__VA_ARGS__ << "] : ["; \ debug_out(__VA_ARGS__); \ std::cerr << "\b\b]\n"; \ } while (false) #else #define debug(...) (void(0)) #endif long long power(long long x, long long n) { // O(logn) // https://algo-logic.info/calc-pow/#toc_id_1_2 long long ret = 1; while (n > 0) { if (n & 1) ret *= x; // n の最下位bitが 1 ならば x^(2^i) をかける x *= x; n >>= 1; // n を1bit 左にずらす } return ret; } // @brief nCr. O(r log n)。あるいは前処理 O(n), 本処理 O(1)で求められる modint // の bc を検討。 int comb(int n, int r) { // https://www.geeksforgeeks.org/program-to-calculate-the-value-of-ncr-efficiently/ if (n < r) return 0; // p holds the value of n*(n-1)*(n-2)..., // k holds the value of r*(r-1)... long long p = 1, k = 1; // C(n, r) == C(n, n-r), // choosing the smaller value if (n - r < r) r = n - r; if (r != 0) { while (r) { p *= n; k *= r; // gcd of p, k long long m = __gcd(p, k); // dividing by gcd, to simplify // product division by their gcd // saves from the overflow p /= m; k /= m; n--; r--; } // k should be simplified to 1 // as C(n, r) is a natural number // (denominator should be 1 ) . } else p = 1; // if our approach is correct p = ans and k =1 return p; } // MOD void add(long long &a, long long b) { a += b; if (a >= MOD) a -= MOD; } template inline bool chmin(T &a, T b) { if (a > b) { a = b; return true; } return false; } template inline bool chmax(T &a, T b) { if (a < b) { a = b; return true; } return false; } // 負数も含む丸め long long ceildiv(long long a, long long b) { if (b < 0) a = -a, b = -b; if (a >= 0) return (a + b - 1) / b; else return a / b; } long long floordiv(long long a, long long b) { if (b < 0) a = -a, b = -b; if (a >= 0) return a / b; else return (a - b + 1) / b; } long long floorsqrt(long long x) { assert(x >= 0); long long ok = 0; long long ng = 1; while (ng * ng <= x) ng <<= 1; while (ng - ok > 1) { long long mid = (ng + ok) >> 1; if (mid * mid <= x) ok = mid; else ng = mid; } return ok; } // @brief a^n mod mod long long modpower(long long a, long long n, long long mod) { long long res = 1; while (n > 0) { if (n & 1) res = res * a % mod; a = a * a % mod; n >>= 1; } return res; } // @brief s が c を含むか template bool contain(const std::string &s, const T &c) { return s.find(c) != std::string::npos; } __attribute__((constructor)) void faster_io() { ios_base::sync_with_stdio(false); cin.tie(nullptr); cerr.tie(nullptr); } /* #endregion */ // ACL はオーバーフローに注意!!! // https://opt-cp.com/digit-dp-implementation/ // https://atcoder.jp/contests/abc154/tasks/abc154_e int n; string s; int K; using mint = modint998244353; signed main() { cin >> n >> s; vector N(n); REP(ni, n) { N[ni] = s[ni] - 'a'; } // dp[i][j][k]:= 上から i-1 桁目 (0-idxed) まで確定させたとき、0 // がちょうど j 個あるようなものの個数。ただし k // のとき、確定させたところまでで N より小さいことが決まっている。 K = 1; vector>> dp( n + 1, vector>(K + 1, vector(2, 0))); dp[0][0][0] = 1; REP(i, n) { int Ni = N[i]; // N の上から i 桁目の数 REP(j, K + 1) { REP(k, 2) { REP(x, 0, 26) { int j2 = j, k2 = k; // 遷移後の状態を表す変数 j2, k2 // を,遷移前の状態で初期化 // 遷移先 j2 を、x, K とかを使って決める if (x == 0) ++j2; // X の上から i 桁目の数字 x が非ゼロなら j2 // を更新 if (j2 > K) continue; // 非ゼロの桁が K より多いなら無視 // 基本いじらない if (!k && (x > Ni)) continue; // X が N より大きいことが確定したら無視 if (x < Ni) k2 = 1; // X が N より小さいことが確定したら k2 を更新 dp[i + 1][j2][k2] += dp[i][j][k]; // i 桁目まで確定 } } } } mint ans = dp[n][K][0] + dp[n][K][1]; int zero = 0; REP(ni, n) { if (N[ni] == 0) zero++; } if (zero == 1) ans--; print(ans.val()); return 0; }