Problem: Consider a road consisting of several rows. Each row is divided into several rectangular tiles, and all tiles in the same row are equal. The first row contains exactly one rectangular tile. Look at the picture below which shows how the tiles are arranged.

The road is constructed as follows: 

  * the first row consists of 1 tile; 
  * then a_1 rows follow; each of these rows contains 1 tile greater than the previous row; 
  * then b_1 rows follow; each of these rows contains 1 tile less than the previous row; 
  * then a_2 rows follow; each of these rows contains 1 tile greater than the previous row; 
  * then b_2 rows follow; each of these rows contains 1 tile less than the previous row; 
  * ... 
  * then a_n rows follow; each of these rows contains 1 tile greater than the previous row; 
  * then b_n rows follow; each of these rows contains 1 tile less than the previous row. 

<image> An example of the road with n = 2, a_1 = 4, b_1 = 2, a_2 = 2, b_2 = 3. Rows are arranged from left to right. 

You start from the only tile in the first row and want to reach the last row (any tile of it). From your current tile, you can move to any tile in the next row which touches your current tile.

Calculate the number of different paths from the first row to the last row. Since it can be large, print it modulo 998244353.

Input

The first line contains one integer n (1 ≤ n ≤ 1000).

Then n lines follow. The i-th of them contains two integers a_i and b_i (1 ≤ a_i, b_i ≤ 10^5; |a_i - b_i| ≤ 5).

Additional constraint on the input: the sequence of a_i and b_i never results in a row with non-positive number of tiles.

Output

Print one integer — the number of paths from the first row to the last row, taken modulo 998244353.

Examples

Input


2
4 2
2 3


Output


850


Input


3
4 1
2 3
3 1


Output


10150


Input


8
328 323
867 868
715 718
721 722
439 435
868 870
834 834
797 796


Output


759099319

Solution (in CPP):

Solution:
#include <bits/stdc++.h>
#ifdef ALGO
#include "el_psy_congroo.hpp"
#else
#define DUMP(...) 1145141919810
#define CHECK(...) (__VA_ARGS__)
#endif

template<int MOD>
struct Integral {
  int v_ = 0;

  template<typename T> Integral(T v) : v_(norm(v)) {  // Implicit conversion is allowed.
    static_assert(std::is_integral<T>::value, "input should be an integral.");
  }
  Integral() = default;
  ~Integral() = default;

  template<typename T> T norm(T v) const {
    if constexpr(std::is_same<long long, T>::value) {
      v %= MOD;
      if (v < 0) v += MOD;
    } else {
      if (v >= MOD) v -= MOD;
      if (v < 0) v += MOD;
      if (v >= MOD || v < 0) {
        v %= MOD;
        if (v < 0) v += MOD;
      }
    }
    return v;
  }

  int val() const { return v_; }
  Integral& operator += (const Integral& rhs) { v_ += rhs.val(); if (v_ >= MOD) v_ -= MOD; return *this; }
  Integral& operator -= (const Integral& rhs) { v_ += MOD - rhs.val(); if (v_ >= MOD) v_ -= MOD; return *this; }
  Integral& operator *= (const Integral& rhs) { v_ = v_ * 1LL * rhs.val() % MOD; return *this; }
  Integral& operator /= (const Integral& rhs) { v_ = v_ * 1LL * power(rhs.val(), MOD - 2) % MOD; return *this; }
  Integral operator + (const Integral& rhs) const { auto copy = *this; return copy += rhs; }
  Integral operator - (const Integral& rhs) const { auto copy = *this; return copy -= rhs; }
  Integral operator * (const Integral& rhs) const { auto copy = *this; return copy *= rhs; }
  Integral operator / (const Integral& rhs) const { auto copy = *this; return copy /= rhs; }
  bool operator == (const Integral& rhs) const { return val() == rhs.val(); }
  bool operator != (const Integral& rhs) const { return !(*this == rhs); }
  const Integral operator - () const { return Integral(-val()); }
  const Integral operator ++ () { v_ = norm(v_ + 1); return *this; }
  const Integral operator ++ (int) { Integral ret = *this; ++(*this); return ret; }
  const Integral operator -- () { v_ = norm(v_ - 1); return *this; }
  const Integral operator -- (int) { Integral ret = *this; --(*this); return ret; }

  Integral power(long long b) const {
    long long ret = 1 % MOD, a = v_;
    for ( ; b; b >>= 1, a = a * a % MOD) if (b & 1) ret = ret * a % MOD; return ret;
  }
  Integral inv() const { return power(MOD - 2); }
};

template<int MOD>
std::string to_string(const Integral<MOD>& v) {
  return std::string("Int<>{") + std::to_string(v.val()) + "}";
}

template<int MOD, bool kAllowBruteForce = false>
struct Binomial {
  std::vector<Integral<MOD>> factor, inv_factor;

  explicit Binomial(int n = 0) : factor(n + 1), inv_factor(n + 1) {
    factor[0] = 1;
    for (int i = 1; i <= n; ++i) factor[i] = factor[i - 1] * i;
    inv_factor[n] = factor[n].inv();
    for (int i = n; i >= 1; --i) inv_factor[i - 1] = inv_factor[i] * i;
  }
  ~Binomial() = default;

  template<typename T>
  Integral<MOD> operator () (T a, T b) const {
    if (a < b || b < 0) return 0;
    if (a < factor.size()) return factor[a] * inv_factor[b] * inv_factor[a - b];
    if constexpr(!kAllowBruteForce) {
      throw std::out_of_range("Binomial");
    } else {
      b = std::min(b, a - b);
      Integral<MOD> ret = 1;
      for (T i = 1; i <= b; ++i) ret = ret * (a + 1 - i) / i;
      return ret;
    }
  }
};

template<int MOD>
struct PowerTable : public std::vector<Integral<MOD>> {
  PowerTable(int n, const Integral<MOD>& g) {
    static_assert(sizeof(PowerTable) == sizeof(std::vector<Integral<MOD>>), "");
    this->resize(n + 1);
    this->at(0) = 1;
    this->at(1) = g;
    for (int i = 2; i < this->size(); ++i) this->at(i) = this->at(i - 1) * this->at(1);
  }
};

const int MOD = 998244353;
using Mint = Integral<MOD>;
using Binom = Binomial<MOD>;

Binom binom(200000);
// PowerTable<MOD> pw2(200000, 2);

template<int MOD = 998244353, int kPrimRoot = 3>
void ntt(Integral<MOD> A[], int n, int inv) {
  // inv == 1: ntt, == -1: intt

  // MOD == a * b ^ k + 1, n <= b ^ k.
  // 998244353 == (7 * 17) * 2 ^ 23 + 1.
  // This code works only when b == 2.
  Integral<MOD> w = 1, d = Integral<MOD>(kPrimRoot).power((MOD - 1) / n), t;
  int i, j, c, s;
  if (inv == -1) {
    for (i = 1, j = n - 1; i < j; ++i, --j) std::swap(A[i], A[j]);
    for (t = Integral<MOD>(n).inv(), i = 0; i < n; ++i) A[i] = A[i] * t;
  }
  for (s = n >> 1; s; s >>= 1, w = 1, d = d * d) {
    for (c = 0; c < s; ++c, w = w * d) {
      for (i = c; i < n; i += s << 1) {
        A[i | s] = (A[i] - (t = A[i | s])) * w;
        A[i] += t;
      }
    }
  }
  for (i = 1; i < n; ++i) {
    for (j = 0, s = i, c = n >> 1; c; c >>= 1, s >>= 1) j = j << 1 | (s & 1);
    if (i < j) std::swap(A[i], A[j]);
  }
}

int main() {
  std::ios::sync_with_stdio(false);
  std::cin.tie(nullptr);
  std::istream& reader = std::cin;

  int n;
  reader >> n;
  std::vector<Mint> f(1, 1);

  for (int at = 1; at <= n; ++at) {
    int a, b;
    reader >> a >> b;
    int m = f.size();
    int w = m + a - b + m + 1;  // b - m, m + a
    int L = 1;
    while (L < m + w) L <<= 1;
    f.resize(L, 0);
    std::vector<Mint> y(L);
    for (int i = 0; i < w; ++i) {
      y[i] = binom(a + b, i + b - m);
    }
    ntt(&f[0], L, 1);
    ntt(&y[0], L, 1);
    for (int i = 0; i < L; ++i) f[i] *= y[i];
    ntt(&f[0], L, -1);
    for (int i = 0; i < m + a - b; ++i) f[i] = i + m < L ? f[i + m] : 0;
    f.resize(m + a - b);
  }
  std::cout << std::accumulate(f.begin(), f.end(), Mint(0)).val() << std::endl;
}