#include <cassert>
#include <cmath>
#include <cstdint>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <algorithm>
#include <bitset>
#include <complex>
#include <deque>
#include <functional>
#include <iostream>
#include <limits>
#include <map>
#include <numeric>
#include <queue>
#include <random>
#include <set>
#include <sstream>
#include <string>
#include <unordered_map>
#include <unordered_set>
#include <utility>
#include <vector>

using namespace std;

using Int = long long;

template <class T1, class T2> ostream &operator<<(ostream &os, const pair<T1, T2> &a) { return os << "(" << a.first << ", " << a.second << ")"; };
template <class T> ostream &operator<<(ostream &os, const vector<T> &as) { const int sz = as.size(); os << "["; for (int i = 0; i < sz; ++i) { if (i >= 256) { os << ", ..."; break; } if (i > 0) { os << ", "; } os << as[i]; } return os << "]"; }
template <class T> void pv(T a, T b) { for (T i = a; i != b; ++i) cerr << *i << " "; cerr << endl; }
template <class T> bool chmin(T &t, const T &f) { if (t > f) { t = f; return true; } return false; }
template <class T> bool chmax(T &t, const T &f) { if (t < f) { t = f; return true; } return false; }
#define COLOR(s) ("\x1b[" s "m")

////////////////////////////////////////////////////////////////////////////////
template <unsigned M_> struct ModInt {
  static constexpr unsigned M = M_;
  unsigned x;
  constexpr ModInt() : x(0U) {}
  constexpr ModInt(unsigned x_) : x(x_ % M) {}
  constexpr ModInt(unsigned long long x_) : x(x_ % M) {}
  constexpr ModInt(int x_) : x(((x_ %= static_cast<int>(M)) < 0) ? (x_ + static_cast<int>(M)) : x_) {}
  constexpr ModInt(long long x_) : x(((x_ %= static_cast<long long>(M)) < 0) ? (x_ + static_cast<long long>(M)) : x_) {}
  ModInt &operator+=(const ModInt &a) { x = ((x += a.x) >= M) ? (x - M) : x; return *this; }
  ModInt &operator-=(const ModInt &a) { x = ((x -= a.x) >= M) ? (x + M) : x; return *this; }
  ModInt &operator*=(const ModInt &a) { x = (static_cast<unsigned long long>(x) * a.x) % M; return *this; }
  ModInt &operator/=(const ModInt &a) { return (*this *= a.inv()); }
  ModInt pow(long long e) const {
    if (e < 0) return inv().pow(-e);
    ModInt a = *this, b = 1U; for (; e; e >>= 1) { if (e & 1) b *= a; a *= a; } return b;
  }
  ModInt inv() const {
    unsigned a = M, b = x; int y = 0, z = 1;
    for (; b; ) { const unsigned q = a / b; const unsigned c = a - q * b; a = b; b = c; const int w = y - static_cast<int>(q) * z; y = z; z = w; }
    assert(a == 1U); return ModInt(y);
  }
  ModInt operator+() const { return *this; }
  ModInt operator-() const { ModInt a; a.x = x ? (M - x) : 0U; return a; }
  ModInt operator+(const ModInt &a) const { return (ModInt(*this) += a); }
  ModInt operator-(const ModInt &a) const { return (ModInt(*this) -= a); }
  ModInt operator*(const ModInt &a) const { return (ModInt(*this) *= a); }
  ModInt operator/(const ModInt &a) const { return (ModInt(*this) /= a); }
  template <class T> friend ModInt operator+(T a, const ModInt &b) { return (ModInt(a) += b); }
  template <class T> friend ModInt operator-(T a, const ModInt &b) { return (ModInt(a) -= b); }
  template <class T> friend ModInt operator*(T a, const ModInt &b) { return (ModInt(a) *= b); }
  template <class T> friend ModInt operator/(T a, const ModInt &b) { return (ModInt(a) /= b); }
  explicit operator bool() const { return x; }
  bool operator==(const ModInt &a) const { return (x == a.x); }
  bool operator!=(const ModInt &a) const { return (x != a.x); }
  friend std::ostream &operator<<(std::ostream &os, const ModInt &a) { return os << a.x; }
};
////////////////////////////////////////////////////////////////////////////////

constexpr unsigned MO = 998244353;
using Mint = ModInt<MO>;


constexpr int INF = 1001001001;

int M;
vector<int> L, R;

int main() {
  for (int numCases; ~scanf("%d", &numCases); ) { for (int caseId = 1; caseId <= numCases; ++caseId) {
    scanf("%*d%d", &M);
    L.resize(M);
    R.resize(M);
    for (int i = 0; i < M; ++i) {
      scanf("%d%d", &L[i], &R[i]);
      --L[i];
    }
    
    vector<int> xs;
    for (int i = 0; i < M; ++i) {
      xs.push_back(L[i]);
      xs.push_back(R[i]);
    }
    sort(xs.begin(), xs.end());
    xs.erase(unique(xs.begin(), xs.end()), xs.end());
    const int N = xs.size();
    for (int i = 0; i < M; ++i) {
      L[i] = lower_bound(xs.begin(), xs.end(), L[i]) - xs.begin();
      R[i] = lower_bound(xs.begin(), xs.end(), R[i]) - xs.begin();
    }
    
    vector<pair<Int, Int>> rats;
    rats.reserve(M * M);
    for (Int p = 1; p <= M; ++p) for (Int q = 1; q <= M; ++q) {
      rats.emplace_back(p, q);
    }
    sort(rats.begin(), rats.end(), [&](const pair<Int, Int> &r0, const pair<Int, Int> &r1) -> bool {
      return (r0.first * r1.second < r1.first * r0.second);
    });
    
    int lo = -1, hi = (int)rats.size();
    for (; lo + 1 < hi; ) {
      const int mid = (lo + hi) / 2;
      const Int p = rats[mid].first;
      const Int q = rats[mid].second;
      bool neg = false;
      vector<Int> dist(N, 0);
      for (int h = 1; h <= N; ++h) {
        bool upd = false;
        for (int u = 0; u < N - 1; ++u) {
          if (chmin(dist[u], dist[u + 1] + 0)) upd = true;
        }
        for (int i = 0; i < M; ++i) {
          if (chmin(dist[R[i]], dist[L[i]] + p)) upd = true;
          if (chmin(dist[L[i]], dist[R[i]] - q)) upd = true;
        }
        if (!upd) break;
        if (h == N) neg = true;
      }
      (neg ? lo : hi) = mid;
    }
    
    assert(hi < (int)rats.size());
    const Int p = rats[hi].first;
    const Int q = rats[hi].second;
// cerr<<p<<"/"<<q<<endl;
    const Mint ans = Mint(p) / Mint(q);
    printf("%u\n", ans.x);
  }
#ifndef LOCAL
  break;
#endif
  }
  return 0;
}