Problem p02632 (C++) — buggy submission, verdict: Runtime Error

#include <bits/stdc++.h>
using namespace std;

// Define
using ll = long long;
using ull = unsigned long long;
using ld = long double;
template <class T> using pvector = vector<pair<T, T>>;
template <class T>
using rpriority_queue = priority_queue<T, vector<T>, greater<T>>;
constexpr const ll dx[4] = {1, 0, -1, 0};
constexpr const ll dy[4] = {0, 1, 0, -1};
constexpr const ll MOD = 1e9 + 7;
constexpr const ll mod = 998244353;
constexpr const ll INF = 1LL << 60;
constexpr const ll inf = 1 << 30;
constexpr const char rt = '\\n';
constexpr const char sp = ' ';
#define mp make_pair
#define mt make_tuple
#define pb push_back
#define eb emplace_back
#define elif else if
#define all(a, v, ...)                                                         \\
  ([&](decltype((v)) w) { return (a)(begin(w), end(w), ##__VA_ARGS__); })(v)
#define rall(a, v, ...)                                                        \\
  ([&](decltype((v)) w) { return (a)(rbegin(w), rend(w), ##__VA_ARGS__); })(v)
#define fi first
#define se second

template <class T> bool chmax(T &a, const T &b) {
  if (a < b) {
    a = b;
    return 1;
  }
  return 0;
}
template <class T> bool chmin(T &a, const T &b) {
  if (a > b) {
    a = b;
    return 1;
  }
  return 0;
}

// Debug
#define debug(...)                                                             \\
  {                                                                            \\
    cerr << __LINE__ << ": " << #__VA_ARGS__ << " = ";                         \\
    for (auto &&X : {__VA_ARGS__})                                             \\
      cerr << "[" << X << "] ";                                                \\
    cerr << rt;                                                                \\
  }

#define dump(a, h, w)                                                          \\
  {                                                                            \\
    cerr << __LINE__ << ": " << #a << " = [" << rt;                            \\
    rep(_i, h) {                                                               \\
      rep(_j, w) {                                                             \\
        if (a[_i][_j] <= -INF / 2)                                             \\
          cerr << '-';                                                         \\
        if (abs(a[_i][_j]) >= INF / 2)                                         \\
          cerr << "∞" << sp;                                                   \\
        else                                                                   \\
          cerr << a[_i][_j] << sp;                                             \\
      }                                                                        \\
      cerr << rt;                                                              \\
    }                                                                          \\
    cerr << "]" << rt;                                                         \\
  }

#define vdump(a, n)                                                            \\
  {                                                                            \\
    cerr << __LINE__ << ": " << #a << " = [";                                  \\
    rep(_i, n) {                                                               \\
      if (_i)                                                                  \\
        cerr << sp;                                                            \\
      if (a[_i] <= -INF / 2)                                                   \\
        cerr << '-';                                                           \\
      if (abs(a[_i]) >= INF / 2)                                               \\
        cerr << "∞" << sp;                                                     \\
      else                                                                     \\
        cerr << a[_i];                                                         \\
    }                                                                          \\
    cerr << "]" << rt;                                                         \\
  }

// Loop
#define inc(i, a, n) for (ll i = (a), _##i = (n); i <= _##i; ++i)
#define dec(i, a, n) for (ll i = (a), _##i = (n); i >= _##i; --i)
#define rep(i, n) for (ll i = 0, _##i = (n); i < _##i; ++i)
#define each(i, a) for (auto &&i : a)

// Stream
#define fout(n) cout << fixed << setprecision(n)
struct io {
  io() { cin.tie(nullptr), ios::sync_with_stdio(false); }
} io;

// Speed
#pragma GCC optimize("Ofast,unroll-loops")
#pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx,tune=native")

// Math
inline constexpr ll gcd(const ll a, const ll b) {
  return b ? gcd(b, a % b) : a;
}
inline constexpr ll lcm(const ll a, const ll b) { return a / gcd(a, b) * b; }

inline constexpr ll modulo(const ll n, const ll m = MOD) {
  ll k = n % m;
  return k + m * (k < 0);
}
inline constexpr ll chmod(ll &n, const ll m = MOD) {
  n %= m;
  return n += m * (n < 0);
}
inline constexpr ll mpow(ll a, ll n, const ll m = MOD) {
  ll r = 1;
  rep(i, 64) {
    if (n & (1LL << i))
      r *= a;
    chmod(r, m);
    a *= a;
    chmod(a, m);
  }
  return r;
}
inline ll inv(const ll n, const ll m = MOD) {
  ll a = n, b = m, x = 1, y = 0;
  while (b) {
    ll t = a / b;
    a -= t * b;
    swap(a, b);
    x -= t * y;
    swap(x, y);
  }
  return modulo(x, m);
}

template <ull mod = MOD> struct mi {
  inline constexpr ll modulo(const ll n, const ll m) const noexcept {
    ll k = n % m;
    return k + m * (k < 0);
  }

  ll num;
  inline constexpr mi() noexcept : num() { num = 0; }
  inline constexpr mi(const int n) noexcept : num() { num = modulo(n, mod); }
  inline constexpr mi(const ll n) noexcept : num() { num = modulo(n, mod); }

  inline constexpr mi<mod> inv() const noexcept {
    ll a = num, b = mod, x = 1, y = 0;
    while (b) {
      ll t = a / b;
      a -= t * b;
      swap(a, b);
      x -= t * y;
      swap(x, y);
    }
    return mi<mod>(x);
  }
  inline constexpr mi<mod> inv(ll n) const noexcept {
    ll a = n, b = mod, x = 1, y = 0;
    while (b) {
      ll t = a / b;
      a -= t * b;
      swap(a, b);
      x -= t * y;
      swap(x, y);
    }
    return mi<mod>(x);
  }
  inline constexpr mi<mod> inv(const mi<mod> m) const noexcept {
    return inv(m.num);
  }

  inline constexpr mi<mod> operator+() const noexcept { return mi(num); }
  inline constexpr mi<mod> operator+(const int n) const noexcept {
    return mi<mod>(num + n);
  }
  inline constexpr mi<mod> operator+(const ll n) const noexcept {
    return mi<mod>(num + n);
  }
  inline constexpr mi<mod> operator+(const mi<mod> m) const noexcept {
    return mi<mod>(num + m.num);
  }
  inline constexpr mi<mod> operator-() const noexcept { return -num; }
  inline constexpr mi<mod> operator-(const int n) const noexcept {
    return mi<mod>(num - n);
  }
  inline constexpr mi<mod> operator-(const ll n) const noexcept {
    return mi<mod>(num - n);
  }
  inline constexpr mi<mod> operator-(const mi<mod> m) const noexcept {
    return mi<mod>(num - m.num);
  }
  inline constexpr mi<mod> operator*(const int n) const noexcept {
    return mi<mod>(num * n);
  }
  inline constexpr mi<mod> operator*(const ll n) const noexcept {
    return mi<mod>(num * n);
  }
  inline constexpr mi<mod> operator*(const mi<mod> m) const noexcept {
    return mi<mod>(num * m);
  }
  inline constexpr mi<mod> operator/(const int n) const noexcept {
    return mi<mod>(num * (ll)inv(n));
  }
  inline constexpr mi<mod> operator/(const ll n) const noexcept {
    return mi<mod>(num * (ll)inv(n));
  }
  inline constexpr mi<mod> operator/(const mi<mod> m) const noexcept {
    return mi<mod>(num * (ll)inv(m));
  }
  inline constexpr mi<mod> &operator=(const int n) noexcept {
    num = modulo(n, mod);
    return *this;
  }
  inline constexpr mi<mod> &operator=(const ll n) noexcept {
    num = modulo(n, mod);
    return *this;
  }
  inline constexpr mi<mod> &operator=(const mi<mod> m) noexcept {
    num = m.num;
    return *this;
  }
  inline constexpr mi<mod> &operator+=(const int n) noexcept {
    num = modulo(num + n, mod);
    return *this;
  }
  inline constexpr mi<mod> &operator+=(const ll n) noexcept {
    num = modulo(num + n, mod);
    return *this;
  }
  inline constexpr mi<mod> &operator+=(const mi<mod> m) noexcept {
    num = modulo(num + m.num, mod);
    return *this;
  }
  inline constexpr mi<mod> &operator++() noexcept {
    num = modulo(num + 1, mod);
    return *this;
  }
  inline constexpr mi<mod> operator++(int) noexcept {
    mi &pre = *this;
    num = modulo(num + 1, mod);
    return pre;
  }
  inline constexpr mi<mod> &operator-=(const int n) noexcept {
    num = modulo(num - n, mod);
    return *this;
  }
  inline constexpr mi<mod> &operator-=(const ll n) noexcept {
    num = modulo(num - n, mod);
    return *this;
  }
  inline constexpr mi<mod> &operator-=(const mi<mod> m) noexcept {
    num = modulo(num - m.num, mod);
    return *this;
  }
  inline constexpr mi<mod> &operator--() noexcept {
    num = modulo(num - 1, mod);
    return *this;
  }
  inline constexpr mi<mod> operator--(int) noexcept {
    mi &pre = *this;
    num = modulo(num - 1, mod);
    return pre;
  }
  inline constexpr mi<mod> &operator*=(const int n) noexcept {
    num = modulo(num * n, mod);
    return *this;
  }
  inline constexpr mi<mod> &operator*=(const ll n) noexcept {
    num = modulo(num * n, mod);
    return *this;
  }
  inline constexpr mi<mod> &operator*=(const mi<mod> m) noexcept {
    num = modulo(num * m.num, mod);
    return *this;
  }
  inline constexpr mi<mod> &operator/=(const int n) noexcept {
    num = modulo(num * (ll)inv(n), mod);
    return *this;
  }
  inline constexpr mi<mod> &operator/=(const ll n) noexcept {
    num = modulo(num * (ll)inv(n), mod);
    return *this;
  }
  inline constexpr mi<mod> &operator/=(const mi<mod> m) noexcept {
    num = modulo(num * (ll)inv(m), mod);
    return *this;
  }
  inline constexpr bool operator==(const int n) const noexcept {
    return num == modulo(n, mod);
  }
  inline constexpr bool operator==(const ll n) const noexcept {
    return num == modulo(n, mod);
  }
  inline constexpr bool operator==(const mi<mod> m) const noexcept {
    return num == m.num;
  }
  inline constexpr bool operator!=(const int n) const noexcept {
    return num != modulo(n, mod);
  }
  inline constexpr bool operator!=(const ll n) const noexcept {
    return num != modulo(n, mod);
  }
  inline constexpr bool operator!=(const mi<mod> m) const noexcept {
    return num != m.num;
  }
  constexpr operator int() const noexcept { return num; }
  constexpr operator ll() const noexcept { return num; }
  friend std::istream &operator>>(std::istream &, const mi<> &);
  friend std::ostream &operator<<(std::ostream &, const mi<> &);
};

template <ull mod = MOD>
inline constexpr mi<mod> operator+(const int n, const mi<mod> m) noexcept {
  return mi<mod>(n + m.num);
}
template <ull mod = MOD>
inline constexpr mi<mod> operator+(const ll n, const mi<mod> m) noexcept {
  return mi<mod>(n + m.num);
}
template <ull mod = MOD>
inline constexpr mi<mod> operator-(const int n, const mi<mod> m) noexcept {
  return mi<mod>(n - m.num);
}
template <ull mod = MOD>
inline constexpr mi<mod> operator-(const ll n, const mi<mod> m) noexcept {
  return mi<mod>(n - m.num);
}
template <ull mod = MOD>
inline constexpr mi<mod> operator*(const int n, const mi<mod> m) noexcept {
  return mi<mod>(n * m.num);
}
template <ull mod = MOD>
inline constexpr mi<mod> operator*(const ll n, const mi<mod> m) noexcept {
  return mi<mod>(n * m.num);
}
template <ull mod = MOD>
inline constexpr mi<mod> operator/(const int n, const mi<mod> m) noexcept {
  return mi<mod>(n * (ll)m.inv());
}
template <ull mod = MOD>
inline constexpr mi<mod> operator/(const ll n, const mi<mod> m) noexcept {
  return mi<mod>(n * (ll)m.inv());
}
inline constexpr mi<MOD> operator""_m(ull n) { return mi<MOD>((ll)n); }

template <ull mod = MOD>
inline constexpr mi<mod> pow(mi<mod> m, ll n) noexcept {
  mi<mod> r = mi<mod>(1);
  rep(i, 64) {
    if (n & (1LL << i))
      r *= m;
    m *= m;
  }
  return r;
}
template <ull mod> istream &operator>>(istream &is, mi<mod> &m) {
  is >> m.num;
  return is;
}
template <ull mod> ostream &operator<<(ostream &is, mi<mod> &m) {
  is << (ll)m;
  return is;
}

template <ull mod = MOD> struct modmath {
  ll max;
  vector<mi<mod>> fac, inv;
  modmath() : max(1 << 21), fac(max + 1), inv(max + 1) {
    fac[0] = mi<mod>(1);
    rep(i, max) fac[i + 1] = fac[i] * (i + 1);
    inv[max] = fac[max].inv();
    dec(i, max - 1, 0) inv[i] = inv[i + 1] * (i + 1);
  }
  modmath(ll n) : max(n), fac(n + 1), inv(n + 1) {
    fac[0] = 1;
    rep(i, n) fac[i + 1] = fac[i] * (i + 1);
    inv[n] = 1 / fac[n];
    dec(i, n - 1, 0) inv[i] = inv[i + 1] * (i + 1);
  }

  inline mi<mod> fact(ll n) {
    if (n < 0)
      return mi<mod>(0);
    return fac[n];
  }
  inline mi<mod> perm(ll n, ll r) {
    if (r < 0 || n < r || n < 0)
      return mi<mod>(0);
    return fac[n] * inv[n - r];
  }
  inline mi<mod> comb(ll n, ll r) {
    if (r < 0 || n < r || n < 0)
      return mi<mod>(0);
    return fac[n] * inv[r] * inv[n - r];
  }
  inline mi<mod> nHr(ll n, ll r) { return comb(n + r - 1, n - 1); }
};

modmath<> math;

signed main() {
  ll K;
  string S;
  cin >> K >> S;
  ll N = S.size();

  mi<> res = mpow(26, K + N);

  inc(i, 0, N - 1) res -= math.comb(K + N, i) * mpow(25, K + N - i);

  cout << res << rt;
}

// -g -D_GLIBCXX_DEBUG -fsanitize=undefined


Error: 0

Fixed submission:

#include <bits/stdc++.h>
using namespace std;

// Define
using ll = long long;
using ull = unsigned long long;
using ld = long double;
template <class T> using pvector = vector<pair<T, T>>;
template <class T>
using rpriority_queue = priority_queue<T, vector<T>, greater<T>>;
constexpr const ll dx[4] = {1, 0, -1, 0};
constexpr const ll dy[4] = {0, 1, 0, -1};
constexpr const ll MOD = 1e9 + 7;
constexpr const ll mod = 998244353;
constexpr const ll INF = 1LL << 60;
constexpr const ll inf = 1 << 30;
constexpr const char rt = '\\n';
constexpr const char sp = ' ';
#define mp make_pair
#define mt make_tuple
#define pb push_back
#define eb emplace_back
#define elif else if
#define all(a, v, ...)                                                         \\
  ([&](decltype((v)) w) { return (a)(begin(w), end(w), ##__VA_ARGS__); })(v)
#define rall(a, v, ...)                                                        \\
  ([&](decltype((v)) w) { return (a)(rbegin(w), rend(w), ##__VA_ARGS__); })(v)
#define fi first
#define se second

template <class T> bool chmax(T &a, const T &b) {
  if (a < b) {
    a = b;
    return 1;
  }
  return 0;
}
template <class T> bool chmin(T &a, const T &b) {
  if (a > b) {
    a = b;
    return 1;
  }
  return 0;
}

// Debug
#define debug(...)                                                             \\
  {                                                                            \\
    cerr << __LINE__ << ": " << #__VA_ARGS__ << " = ";                         \\
    for (auto &&X : {__VA_ARGS__})                                             \\
      cerr << "[" << X << "] ";                                                \\
    cerr << rt;                                                                \\
  }

#define dump(a, h, w)                                                          \\
  {                                                                            \\
    cerr << __LINE__ << ": " << #a << " = [" << rt;                            \\
    rep(_i, h) {                                                               \\
      rep(_j, w) {                                                             \\
        if (a[_i][_j] <= -INF / 2)                                             \\
          cerr << '-';                                                         \\
        if (abs(a[_i][_j]) >= INF / 2)                                         \\
          cerr << "∞" << sp;                                                   \\
        else                                                                   \\
          cerr << a[_i][_j] << sp;                                             \\
      }                                                                        \\
      cerr << rt;                                                              \\
    }                                                                          \\
    cerr << "]" << rt;                                                         \\
  }

#define vdump(a, n)                                                            \\
  {                                                                            \\
    cerr << __LINE__ << ": " << #a << " = [";                                  \\
    rep(_i, n) {                                                               \\
      if (_i)                                                                  \\
        cerr << sp;                                                            \\
      if (a[_i] <= -INF / 2)                                                   \\
        cerr << '-';                                                           \\
      if (abs(a[_i]) >= INF / 2)                                               \\
        cerr << "∞" << sp;                                                     \\
      else                                                                     \\
        cerr << a[_i];                                                         \\
    }                                                                          \\
    cerr << "]" << rt;                                                         \\
  }

// Loop
#define inc(i, a, n) for (ll i = (a), _##i = (n); i <= _##i; ++i)
#define dec(i, a, n) for (ll i = (a), _##i = (n); i >= _##i; --i)
#define rep(i, n) for (ll i = 0, _##i = (n); i < _##i; ++i)
#define each(i, a) for (auto &&i : a)

// Stream
#define fout(n) cout << fixed << setprecision(n)
struct io {
  io() { cin.tie(nullptr), ios::sync_with_stdio(false); }
} io;

// Speed
#pragma GCC optimize("Ofast,unroll-loops")
#pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx,tune=native")

// Math
inline constexpr ll gcd(const ll a, const ll b) {
  return b ? gcd(b, a % b) : a;
}
inline constexpr ll lcm(const ll a, const ll b) { return a / gcd(a, b) * b; }

inline constexpr ll modulo(const ll n, const ll m = MOD) {
  ll k = n % m;
  return k + m * (k < 0);
}
inline constexpr ll chmod(ll &n, const ll m = MOD) {
  n %= m;
  return n += m * (n < 0);
}
inline constexpr ll mpow(ll a, ll n, const ll m = MOD) {
  ll r = 1;
  rep(i, 64) {
    if (n & (1LL << i))
      r *= a;
    chmod(r, m);
    a *= a;
    chmod(a, m);
  }
  return r;
}
inline ll inv(const ll n, const ll m = MOD) {
  ll a = n, b = m, x = 1, y = 0;
  while (b) {
    ll t = a / b;
    a -= t * b;
    swap(a, b);
    x -= t * y;
    swap(x, y);
  }
  return modulo(x, m);
}

template <ull mod = MOD> struct mi {
  inline constexpr ll modulo(const ll n, const ll m) const noexcept {
    ll k = n % m;
    return k + m * (k < 0);
  }

  ll num;
  inline constexpr mi() noexcept : num() { num = 0; }
  inline constexpr mi(const int n) noexcept : num() { num = modulo(n, mod); }
  inline constexpr mi(const ll n) noexcept : num() { num = modulo(n, mod); }

  inline constexpr mi<mod> inv() const noexcept {
    ll a = num, b = mod, x = 1, y = 0;
    while (b) {
      ll t = a / b;
      a -= t * b;
      swap(a, b);
      x -= t * y;
      swap(x, y);
    }
    return mi<mod>(x);
  }
  inline constexpr mi<mod> inv(ll n) const noexcept {
    ll a = n, b = mod, x = 1, y = 0;
    while (b) {
      ll t = a / b;
      a -= t * b;
      swap(a, b);
      x -= t * y;
      swap(x, y);
    }
    return mi<mod>(x);
  }
  inline constexpr mi<mod> inv(const mi<mod> m) const noexcept {
    return inv(m.num);
  }

  inline constexpr mi<mod> operator+() const noexcept { return mi(num); }
  inline constexpr mi<mod> operator+(const int n) const noexcept {
    return mi<mod>(num + n);
  }
  inline constexpr mi<mod> operator+(const ll n) const noexcept {
    return mi<mod>(num + n);
  }
  inline constexpr mi<mod> operator+(const mi<mod> m) const noexcept {
    return mi<mod>(num + m.num);
  }
  inline constexpr mi<mod> operator-() const noexcept { return -num; }
  inline constexpr mi<mod> operator-(const int n) const noexcept {
    return mi<mod>(num - n);
  }
  inline constexpr mi<mod> operator-(const ll n) const noexcept {
    return mi<mod>(num - n);
  }
  inline constexpr mi<mod> operator-(const mi<mod> m) const noexcept {
    return mi<mod>(num - m.num);
  }
  inline constexpr mi<mod> operator*(const int n) const noexcept {
    return mi<mod>(num * n);
  }
  inline constexpr mi<mod> operator*(const ll n) const noexcept {
    return mi<mod>(num * n);
  }
  inline constexpr mi<mod> operator*(const mi<mod> m) const noexcept {
    return mi<mod>(num * m);
  }
  inline constexpr mi<mod> operator/(const int n) const noexcept {
    return mi<mod>(num * (ll)inv(n));
  }
  inline constexpr mi<mod> operator/(const ll n) const noexcept {
    return mi<mod>(num * (ll)inv(n));
  }
  inline constexpr mi<mod> operator/(const mi<mod> m) const noexcept {
    return mi<mod>(num * (ll)inv(m));
  }
  inline constexpr mi<mod> &operator=(const int n) noexcept {
    num = modulo(n, mod);
    return *this;
  }
  inline constexpr mi<mod> &operator=(const ll n) noexcept {
    num = modulo(n, mod);
    return *this;
  }
  inline constexpr mi<mod> &operator=(const mi<mod> m) noexcept {
    num = m.num;
    return *this;
  }
  inline constexpr mi<mod> &operator+=(const int n) noexcept {
    num = modulo(num + n, mod);
    return *this;
  }
  inline constexpr mi<mod> &operator+=(const ll n) noexcept {
    num = modulo(num + n, mod);
    return *this;
  }
  inline constexpr mi<mod> &operator+=(const mi<mod> m) noexcept {
    num = modulo(num + m.num, mod);
    return *this;
  }
  inline constexpr mi<mod> &operator++() noexcept {
    num = modulo(num + 1, mod);
    return *this;
  }
  inline constexpr mi<mod> operator++(int) noexcept {
    mi &pre = *this;
    num = modulo(num + 1, mod);
    return pre;
  }
  inline constexpr mi<mod> &operator-=(const int n) noexcept {
    num = modulo(num - n, mod);
    return *this;
  }
  inline constexpr mi<mod> &operator-=(const ll n) noexcept {
    num = modulo(num - n, mod);
    return *this;
  }
  inline constexpr mi<mod> &operator-=(const mi<mod> m) noexcept {
    num = modulo(num - m.num, mod);
    return *this;
  }
  inline constexpr mi<mod> &operator--() noexcept {
    num = modulo(num - 1, mod);
    return *this;
  }
  inline constexpr mi<mod> operator--(int) noexcept {
    mi &pre = *this;
    num = modulo(num - 1, mod);
    return pre;
  }
  inline constexpr mi<mod> &operator*=(const int n) noexcept {
    num = modulo(num * n, mod);
    return *this;
  }
  inline constexpr mi<mod> &operator*=(const ll n) noexcept {
    num = modulo(num * n, mod);
    return *this;
  }
  inline constexpr mi<mod> &operator*=(const mi<mod> m) noexcept {
    num = modulo(num * m.num, mod);
    return *this;
  }
  inline constexpr mi<mod> &operator/=(const int n) noexcept {
    num = modulo(num * (ll)inv(n), mod);
    return *this;
  }
  inline constexpr mi<mod> &operator/=(const ll n) noexcept {
    num = modulo(num * (ll)inv(n), mod);
    return *this;
  }
  inline constexpr mi<mod> &operator/=(const mi<mod> m) noexcept {
    num = modulo(num * (ll)inv(m), mod);
    return *this;
  }
  inline constexpr bool operator==(const int n) const noexcept {
    return num == modulo(n, mod);
  }
  inline constexpr bool operator==(const ll n) const noexcept {
    return num == modulo(n, mod);
  }
  inline constexpr bool operator==(const mi<mod> m) const noexcept {
    return num == m.num;
  }
  inline constexpr bool operator!=(const int n) const noexcept {
    return num != modulo(n, mod);
  }
  inline constexpr bool operator!=(const ll n) const noexcept {
    return num != modulo(n, mod);
  }
  inline constexpr bool operator!=(const mi<mod> m) const noexcept {
    return num != m.num;
  }
  constexpr operator int() const noexcept { return num; }
  constexpr operator ll() const noexcept { return num; }
  friend std::istream &operator>>(std::istream &, const mi<> &);
  friend std::ostream &operator<<(std::ostream &, const mi<> &);
};

template <ull mod = MOD>
inline constexpr mi<mod> operator+(const int n, const mi<mod> m) noexcept {
  return mi<mod>(n + m.num);
}
template <ull mod = MOD>
inline constexpr mi<mod> operator+(const ll n, const mi<mod> m) noexcept {
  return mi<mod>(n + m.num);
}
template <ull mod = MOD>
inline constexpr mi<mod> operator-(const int n, const mi<mod> m) noexcept {
  return mi<mod>(n - m.num);
}
template <ull mod = MOD>
inline constexpr mi<mod> operator-(const ll n, const mi<mod> m) noexcept {
  return mi<mod>(n - m.num);
}
template <ull mod = MOD>
inline constexpr mi<mod> operator*(const int n, const mi<mod> m) noexcept {
  return mi<mod>(n * m.num);
}
template <ull mod = MOD>
inline constexpr mi<mod> operator*(const ll n, const mi<mod> m) noexcept {
  return mi<mod>(n * m.num);
}
template <ull mod = MOD>
inline constexpr mi<mod> operator/(const int n, const mi<mod> m) noexcept {
  return mi<mod>(n * (ll)m.inv());
}
template <ull mod = MOD>
inline constexpr mi<mod> operator/(const ll n, const mi<mod> m) noexcept {
  return mi<mod>(n * (ll)m.inv());
}
inline constexpr mi<MOD> operator""_m(ull n) { return mi<MOD>((ll)n); }

template <ull mod = MOD>
inline constexpr mi<mod> pow(mi<mod> m, ll n) noexcept {
  mi<mod> r = mi<mod>(1);
  rep(i, 64) {
    if (n & (1LL << i))
      r *= m;
    m *= m;
  }
  return r;
}
template <ull mod> istream &operator>>(istream &is, mi<mod> &m) {
  is >> m.num;
  return is;
}
template <ull mod> ostream &operator<<(ostream &is, mi<mod> &m) {
  is << (ll)m;
  return is;
}

template <ull mod = MOD> struct modmath {
  ll max;
  vector<mi<mod>> fac, inv;
  modmath() : max(1 << 20), fac(max + 1), inv(max + 1) {
    fac[0] = mi<mod>(1);
    rep(i, max) fac[i + 1] = fac[i] * (i + 1);
    inv[max] = fac[max].inv();
    dec(i, max - 1, 0) inv[i] = inv[i + 1] * (i + 1);
  }
  modmath(ll n) : max(n), fac(n + 1), inv(n + 1) {
    fac[0] = 1;
    rep(i, n) fac[i + 1] = fac[i] * (i + 1);
    inv[n] = 1 / fac[n];
    dec(i, n - 1, 0) inv[i] = inv[i + 1] * (i + 1);
  }

  inline mi<mod> fact(ll n) {
    if (n < 0)
      return mi<mod>(0);
    return fac[n];
  }
  inline mi<mod> perm(ll n, ll r) {
    if (r < 0 || n < r || n < 0)
      return mi<mod>(0);
    return fac[n] * inv[n - r];
  }
  inline mi<mod> comb(ll n, ll r) {
    if (r < 0 || n < r || n < 0)
      return mi<mod>(0);
    return fac[n] * inv[r] * inv[n - r];
  }
  inline mi<mod> nHr(ll n, ll r) { return comb(n + r - 1, n - 1); }
};

signed main() {
  ll K;
  string S;
  cin >> K >> S;
  ll N = S.size();
  modmath<> math;
  mi<> res = mpow(26, K + N);

  inc(i, 0, N - 1) res -= math.comb(K + N, i) * mpow(25, K + N - i);

  cout << res << rt;
}

// -g -D_GLIBCXX_DEBUG -fsanitize=undefined