#include <bits/stdc++.h>
using namespace std;
template <class T>
void chmin(T &a, const T &b) {
  if (a > b) a = b;
}
template <class T>
void chmax(T &a, const T &b) {
  if (a < b) a = b;
}
template <class T>
using MaxHeap = priority_queue<T>;
template <class T>
using MinHeap = priority_queue<T, vector<T>, greater<T>>;
template <class T>
vector<T> vect(int len, T elem) {
  return vector<T>(len, elem);
}
template <class T, class U>
ostream &operator<<(ostream &os, const pair<T, U> &p) {
  os << p.first << ',' << p.second;
  return os;
}
template <class T, class U>
istream &operator>>(istream &is, pair<T, U> &p) {
  is >> p.first >> p.second;
  return is;
}
template <class T>
ostream &operator<<(ostream &os, const vector<T> &vec) {
  for (int i = 0; i < vec.size(); i++) {
    os << vec[i];
    if (i + 1 < vec.size()) os << ' ';
  }
  return os;
}
template <class T>
istream &operator>>(istream &is, vector<T> &vec) {
  for (int i = 0; i < vec.size(); i++) is >> vec[i];
  return is;
}
void fastio() {
  cin.tie(0);
  ios::sync_with_stdio(0);
  cout << fixed << setprecision(20);
}
template <int MOD>
struct ModInt {
  long long val;
  ModInt() : val(0ll) {}
  ModInt(const long long &v) : val(((v % MOD) + MOD) % MOD) {}
  bool operator==(const ModInt &x) const { return val == x.val; }
  bool operator!=(const ModInt &x) const { return !(*this == x); }
  bool operator<(const ModInt &x) const { return val < x.val; }
  bool operator>(const ModInt &x) const { return val > x.val; }
  bool operator>=(const ModInt &x) const { return !(*this < x); }
  bool operator<=(const ModInt &x) const { return !(*this > x); }
  ModInt operator-() const { return ModInt(MOD - val); }
  ModInt inv() const { return this->pow(MOD - 2); }
  ModInt &operator+=(const ModInt &x) {
    if ((val += x.val) >= MOD) val -= MOD;
    return *this;
  }
  ModInt &operator-=(const ModInt &x) {
    if ((val += MOD - x.val) >= MOD) val -= MOD;
    return *this;
  }
  ModInt &operator*=(const ModInt &x) {
    (val *= x.val) %= MOD;
    return *this;
  }
  ModInt &operator/=(const ModInt &x) { return *this *= x.inv(); };
  ModInt operator+(const ModInt &x) const { return ModInt(*this) += x; }
  ModInt operator-(const ModInt &x) const { return ModInt(*this) -= x; }
  ModInt operator*(const ModInt &x) const { return ModInt(*this) *= x; }
  ModInt operator/(const ModInt &x) const { return ModInt(*this) /= x; }
  friend istream &operator>>(istream &i, ModInt &x) {
    long long v;
    i >> v;
    x = v;
    return i;
  }
  friend ostream &operator<<(ostream &o, const ModInt &x) {
    o << x.val;
    return o;
  }
  ModInt pow(long long x) const {
    auto res = ModInt(1ll);
    auto b = *this;
    while (x) {
      if (x & 1) res *= b;
      x >>= 1;
      b *= b;
    }
    return res;
  }
};
template <int MOD>
ModInt<MOD> pow(ModInt<MOD> a, long long x) {
  ModInt<MOD> res = ModInt<MOD>(1ll);
  while (x) {
    if (x & 1) res *= a;
    x >>= 1;
    a *= a;
  }
  return res;
}
constexpr int MOD = 998244353;
using mint = ModInt<MOD>;
vector<mint> inv, fac, facinv;
mint nCr(int n, int r) {
  assert(!(n < r));
  assert(!(n < 0 || r < 0));
  return fac[n] * facinv[r] * facinv[n - r];
}
void init(int SIZE) {
  fac.resize(SIZE + 1);
  inv.resize(SIZE + 1);
  facinv.resize(SIZE + 1);
  fac[0] = inv[1] = facinv[0] = mint(1ll);
  for (int i = 1; i <= SIZE; i++) fac[i] = fac[i - 1] * mint(i);
  for (int i = 2; i <= SIZE; i++)
    inv[i] = mint(0ll) - mint(MOD / i) * inv[MOD % i];
  for (int i = 1; i <= SIZE; i++) facinv[i] = facinv[i - 1] * inv[i];
  return;
}
void solve() {
  int n;
  cin >> n;
  string s;
  cin >> s;
  long long l = 0;
  while (s[l] == s[0]) l++;
  long long r = 0;
  while (s[n - 1 - r] == s[n - 1]) r++;
  if (s[0] != s[n - 1]) {
    cout << (l + r + 1) % MOD << "\n";
  } else {
    cout << ((l + 1) * (r + 1)) % MOD << "\n";
  }
  return;
}
signed main() {
  fastio();
  solve();
  return 0;
}
