#include<bits/stdc++.h>
using namespace std;
using Int = long long;
template<typename T1,typename T2> inline void chmin(T1 &a,T2 b){if(a>b) a=b;}
template<typename T1,typename T2> inline void chmax(T1 &a,T2 b){if(a<b) a=b;}


struct FastIO{
  FastIO(){
    cin.tie(0);
    ios::sync_with_stdio(0);
  }
}fastio_beet;


template<typename T,T MOD = 1000000007>
struct Mint{
  static constexpr T mod = MOD;
  T v;
  Mint():v(0){}
  Mint(signed v):v(v){}
  Mint(long long t){v=t%MOD;if(v<0) v+=MOD;}

  Mint pow(long long k){
    Mint res(1),tmp(v);
    while(k){
      if(k&1) res*=tmp;
      tmp*=tmp;
      k>>=1;
    }
    return res;
  }

  static Mint add_identity(){return Mint(0);}
  static Mint mul_identity(){return Mint(1);}

  Mint inv(){return pow(MOD-2);}

  Mint& operator+=(Mint a){v+=a.v;if(v>=MOD)v-=MOD;return *this;}
  Mint& operator-=(Mint a){v+=MOD-a.v;if(v>=MOD)v-=MOD;return *this;}
  Mint& operator*=(Mint a){v=1LL*v*a.v%MOD;return *this;}
  Mint& operator/=(Mint a){return (*this)*=a.inv();}

  Mint operator+(Mint a) const{return Mint(v)+=a;};
  Mint operator-(Mint a) const{return Mint(v)-=a;};
  Mint operator*(Mint a) const{return Mint(v)*=a;};
  Mint operator/(Mint a) const{return Mint(v)/=a;};

  Mint operator-() const{return v?Mint(MOD-v):Mint(v);}

  bool operator==(const Mint a)const{return v==a.v;}
  bool operator!=(const Mint a)const{return v!=a.v;}
  bool operator <(const Mint a)const{return v <a.v;}

  static Mint comb(long long n,Int k){
    Mint num(1),dom(1);
    for(Int i=0;i<k;i++){
      num*=Mint(n-i);
      dom*=Mint(i+1);
    }
    return num/dom;
  }
};
template<typename T,T MOD> constexpr T Mint<T, MOD>::mod;
template<typename T,T MOD>
ostream& operator<<(ostream &os,Mint<T, MOD> m){os<<m.v;return os;}


template<typename V>
V compress(V v){
  sort(v.begin(),v.end());
  v.erase(unique(v.begin(),v.end()),v.end());
  return v;
}
template<typename T>
map<T, Int> dict(const vector<T> &v){
  map<T, Int> res;
  for(Int i=0;i<(Int)v.size();i++)
    res[v[i]]=i;
  return res;
}
map<char, Int> dict(const string &v){
  return dict(vector<char>(v.begin(),v.end()));
}

template<typename T>
struct FormalPowerSeries{
  using Poly = vector<T>;
  using Conv = function<Poly(Poly, Poly)>;
  Conv conv;
  FormalPowerSeries(Conv conv):conv(conv){}

  Poly pre(const Poly &as,Int deg){
    return Poly(as.begin(),as.begin()+min((Int)as.size(),deg));
  }

  Poly add(Poly as,Poly bs){
    Int sz=max(as.size(),bs.size());
    Poly cs(sz,T(0));
    for(Int i=0;i<(Int)as.size();i++) cs[i]+=as[i];
    for(Int i=0;i<(Int)bs.size();i++) cs[i]+=bs[i];
    return cs;
  }

  Poly sub(Poly as,Poly bs){
    Int sz=max(as.size(),bs.size());
    Poly cs(sz,T(0));
    for(Int i=0;i<(Int)as.size();i++) cs[i]+=as[i];
    for(Int i=0;i<(Int)bs.size();i++) cs[i]-=bs[i];
    return cs;
  }

  Poly mul(Poly as,Poly bs){
    return conv(as,bs);
  }

  Poly mul(Poly as,T k){
    for(auto &a:as) a*=k;
    return as;
  }

  // F(0) must not be 0
  Poly inv(Poly as,Int deg){
    assert(as[0]!=T(0));
    Poly rs({T(1)/as[0]});
    for(Int i=1;i<deg;i<<=1)
      rs=pre(sub(add(rs,rs),mul(mul(rs,rs),pre(as,i<<1))),i<<1);
    return rs;
  }

  // not zero
  Poly div(Poly as,Poly bs){
    while(as.back()==T(0)) as.pop_back();
    while(bs.back()==T(0)) bs.pop_back();
    if(bs.size()>as.size()) return Poly();
    reverse(as.begin(),as.end());
    reverse(bs.begin(),bs.end());
    Int need=as.size()-bs.size()+1;
    Poly ds=pre(mul(as,inv(bs,need)),need);
    reverse(ds.begin(),ds.end());
    return ds;
  }

  // F(0) must be 1
  Poly sqrt(Poly as,Int deg){
    assert(as[0]==T(1));
    T inv2=T(1)/T(2);
    Poly ss({T(1)});
    for(Int i=1;i<deg;i<<=1){
      ss=pre(add(ss,mul(pre(as,i<<1),inv(ss,i<<1))),i<<1);
      for(T &x:ss) x*=inv2;
    }
    return ss;
  }

  Poly diff(Poly as){
    Int n=as.size();
    Poly rs(n-1);
    for(Int i=1;i<n;i++) rs[i-1]=as[i]*T(i);
    return rs;
  }

  Poly integral(Poly as){
    Int n=as.size();
    Poly rs(n+1);
    rs[0]=T(0);
    for(Int i=0;i<n;i++) rs[i+1]=as[i]/T(i+1);
    return rs;
  }

  // F(0) must be 1
  Poly log(Poly as,Int deg){
    return pre(integral(mul(diff(as),inv(as,deg))),deg);
  }

  // F(0) must be 0
  Poly exp(Poly as,Int deg){
    Poly f({T(1)});
    as[0]+=T(1);
    for(Int i=1;i<deg;i<<=1)
      f=pre(mul(f,sub(pre(as,i<<1),log(f,i<<1))),i<<1);
    return f;
  }

  Poly partition(Int n){
    Poly rs(n+1);
    rs[0]=T(1);
    for(Int k=1;k<=n;k++){
      if(1LL*k*(3*k+1)/2<=n) rs[k*(3*k+1)/2]+=T(k%2?-1LL:1LL);
      if(1LL*k*(3*k-1)/2<=n) rs[k*(3*k-1)/2]+=T(k%2?-1LL:1LL);
    }
    return inv(rs,n+1);
  }

  Poly bernoulli(Int n){
    Poly rs(n+1,1);
    for(Int i=1;i<=n;i++) rs[i]=rs[i-1]/T(i+1);
    rs=inv(rs,n+1);
    T tmp(1);
    for(Int i=1;i<=n;i++){
      tmp*=T(i);
      rs[i]*=tmp;
    }
    return rs;
  }
};


template<typename M>
class Enumeration{
private:
  static vector<M> fact,finv,invs;
public:
  static void init(Int n){
    n=min<decltype(M::mod)>(n,M::mod-1);

    Int m=fact.size();
    if(n<m) return;

    fact.resize(n+1,1);
    finv.resize(n+1,1);
    invs.resize(n+1,1);

    if(m==0) m=1;
    for(Int i=m;i<=n;i++) fact[i]=fact[i-1]*M(i);
    finv[n]=M(1)/fact[n];
    for(Int i=n;i>=m;i--) finv[i-1]=finv[i]*M(i);
    for(Int i=m;i<=n;i++) invs[i]=finv[i]*fact[i-1];
  }

  static M Fact(Int n){
    init(n);
    return fact[n];
  }
  static M Finv(Int n){
    init(n);
    return finv[n];
  }
  static M Invs(Int n){
    init(n);
    return invs[n];
  }

  static M C(Int n,Int k){
    if(n<k||k<0) return M(0);
    init(n);
    return fact[n]*finv[n-k]*finv[k];
  }

  static M P(Int n,Int k){
    if(n<k||k<0) return M(0);
    init(n);
    return fact[n]*finv[n-k];
  }

  static M H(Int n,Int k){
    if(n<0||k<0) return M(0);
    if(!n&&!k) return M(1);
    init(n+k-1);
    return C(n+k-1,k);
  }

  static M S(Int n,Int k){
    init(k);
    M res(0);
    for(Int i=1;i<=k;i++){
      M tmp=C(k,i)*M(i).pow(n);
      if((k-i)&1) res-=tmp;
      else res+=tmp;
    }
    return res*=finv[k];
  }

  static vector< vector<M> > D(Int n,Int m){
    vector< vector<M> > dp(n+1,vector<M>(m+1,0));
    dp[0][0]=M(1);
    for(Int i=0;i<=n;i++){
      for(Int j=1;j<=m;j++){
        if(i-j>=0) dp[i][j]=dp[i][j-1]+dp[i-j][j];
        else dp[i][j]=dp[i][j-1];
      }
    }
    return dp;
  }

  static M B(Int n,Int k){
    if(n==0) return M(1);
    k=min(k,n);
    init(k);
    vector<M> dp(k+1);
    dp[0]=M(1);
    for(Int i=1;i<=k;i++)
      dp[i]=dp[i-1]+((i&1)?-finv[i]:finv[i]);
    M res(0);
    for(Int i=1;i<=k;i++)
      res+=M(i).pow(n)*finv[i]*dp[k-i];
    return res;
  }

  static M montmort(Int n){
    init(n);
    M res(0);
    for(Int k=2;k<=n;k++){
      if(k&1) res-=finv[k];
      else res+=finv[k];
    }
    return res*=fact[n];
  }

  static M LagrangePolynomial(vector<M> &y,M t){
    Int n=y.size()-1;
    if(t.v<=n) return y[t.v];
    init(n+1);
    vector<M> dp(n+1,1),pd(n+1,1);
    for(Int i=0;i<n;i++) dp[i+1]=dp[i]*(t-M(i));
    for(Int i=n;i>0;i--) pd[i-1]=pd[i]*(t-M(i));
    M res(0);
    for(Int i=0;i<=n;i++){
      M tmp=y[i]*dp[i]*pd[i]*finv[i]*finv[n-i];
      if((n-i)&1) res-=tmp;
      else res+=tmp;
    }
    return res;
  }
};
template<typename M>
vector<M> Enumeration<M>::fact=vector<M>();
template<typename M>
vector<M> Enumeration<M>::finv=vector<M>();
template<typename M>
vector<M> Enumeration<M>::invs=vector<M>();


constexpr Int bmds(Int x){
  const Int v[] = {1012924417, 924844033, 998244353,
                   897581057, 645922817};
  return v[x];
}
constexpr Int brts(Int x){
  const Int v[] = {5, 5, 3, 3, 3};
  return v[x];
}

template<Int X>
struct NTT{
  static constexpr Int md = bmds(X);
  static constexpr Int rt = brts(X);
  using M = Mint<Int, md>;
  vector< vector<M> > rts,rrts;

  void ensure_base(Int n){
    if((Int)rts.size()>=n) return;
    rts.resize(n);rrts.resize(n);
    for(Int i=1;i<n;i<<=1){
      if(!rts[i].empty()) continue;
      M w=M(rt).pow((md-1)/(i<<1));
      M rw=w.inv();
      rts[i].resize(i);rrts[i].resize(i);
      rts[i][0]=M(1);rrts[i][0]=M(1);
      for(Int k=1;k<i;k++){
        rts[i][k]=rts[i][k-1]*w;
        rrts[i][k]=rrts[i][k-1]*rw;
      }
    }
  }

  void ntt(vector<M> &as,bool f,Int n=-1){
    if(n==-1) n=as.size();
    assert((n&(n-1))==0);
    ensure_base(n);

    for(Int i=0,j=1;j+1<n;j++){
      for(Int k=n>>1;k>(i^=k);k>>=1);
      if(i>j) swap(as[i],as[j]);
    }

    for(Int i=1;i<n;i<<=1){
      for(Int j=0;j<n;j+=i*2){
        for(Int k=0;k<i;k++){
          M z=as[i+j+k]*(f?rrts[i][k]:rts[i][k]);
          as[i+j+k]=as[j+k]-z;
          as[j+k]+=z;
        }
      }
    }

    if(f){
      M tmp=M(n).inv();
      for(Int i=0;i<n;i++) as[i]*=tmp;
    }
  }

  vector<M> multiply(vector<M> as,vector<M> bs){
    Int need=as.size()+bs.size()-1;
    Int sz=1;
    while(sz<need) sz<<=1;
    as.resize(sz,M(0));
    bs.resize(sz,M(0));

    ntt(as,0);ntt(bs,0);
    for(Int i=0;i<sz;i++) as[i]*=bs[i];
    ntt(as,1);

    as.resize(need);
    return as;
  }

  vector<Int> multiply(vector<Int> as,vector<Int> bs){
    vector<M> am(as.size()),bm(bs.size());
    for(Int i=0;i<(Int)am.size();i++) am[i]=M(as[i]);
    for(Int i=0;i<(Int)bm.size();i++) bm[i]=M(bs[i]);
    vector<M> cm=multiply(am,bm);
    vector<Int> cs(cm.size());
    for(Int i=0;i<(Int)cs.size();i++) cs[i]=cm[i].v;
    return cs;
  }
};
template<Int X> constexpr Int NTT<X>::md;
template<Int X> constexpr Int NTT<X>::rt;


struct ArbitraryModConvolution{
  using ll = long long;
  static NTT<0> ntt0;
  static NTT<1> ntt1;
  static NTT<2> ntt2;

  static constexpr Int pow(Int a,Int b,Int md){
    Int res=1;
    a=a%md;
    while(b){
      if(b&1) res=(ll)res*a%md;
      a=(ll)a*a%md;
      b>>=1;
    }
    return res;
  }

  static constexpr Int inv(Int x,Int md){
    return pow(x,md-2,md);
  }

  inline void garner(Int &c0,Int c1,Int c2,Int m01,Int MOD){
    static constexpr Int r01=inv(ntt0.md,ntt1.md);
    static constexpr Int r02=inv(ntt0.md,ntt2.md);
    static constexpr Int r12=inv(ntt1.md,ntt2.md);

    c1=(ll)(c1-c0)*r01%ntt1.md;
    if(c1<0) c1+=ntt1.md;

    c2=(ll)(c2-c0)*r02%ntt2.md;
    c2=(ll)(c2-c1)*r12%ntt2.md;
    if(c2<0) c2+=ntt2.md;

    c0+=(ll)c1*ntt0.md%MOD;
    if(c0>=MOD) c0-=MOD;
    c0+=(ll)c2*m01%MOD;
    if(c0>=MOD) c0-=MOD;
  }

  inline void garner(vector< vector<Int> > &cs,Int MOD){
    Int m01 =(ll)ntt0.md*ntt1.md%MOD;
    Int sz=cs[0].size();
    for(Int i=0;i<sz;i++) garner(cs[0][i],cs[1][i],cs[2][i],m01,MOD);
  }

  vector<Int> multiply(vector<Int> as,vector<Int> bs,Int MOD){
    vector< vector<Int> > cs(3);
    cs[0]=ntt0.multiply(as,bs);
    cs[1]=ntt1.multiply(as,bs);
    cs[2]=ntt2.multiply(as,bs);
    size_t sz=as.size()+bs.size()-1;
    for(auto& v:cs) v.resize(sz);
    garner(cs,MOD);
    return cs[0];
  }

  template<typename T,T MOD>
  decltype(auto) multiply(vector< Mint<T, MOD> > am,
                          vector< Mint<T, MOD> > bm){
    using M = Mint<T, MOD>;
    vector<Int> as(am.size()),bs(bm.size());
    for(Int i=0;i<(Int)as.size();i++) as[i]=am[i].v;
    for(Int i=0;i<(Int)bs.size();i++) bs[i]=bm[i].v;
    vector<Int> cs=multiply(as,bs,MOD);
    vector<M> cm(cs.size());
    for(Int i=0;i<(Int)cm.size();i++) cm[i]=M(cs[i]);
    return cm;
  }
};
NTT<0> ArbitraryModConvolution::ntt0;
NTT<1> ArbitraryModConvolution::ntt1;
NTT<2> ArbitraryModConvolution::ntt2;

//INSERT ABOVE HERE
signed main(){
  Int n;
  cin>>n;
  vector<Int> as(n),bs(n);
  for(Int i=0;i<n;i++) cin>>as[i]>>bs[i];

  vector<Int> vs;
  for(Int a:as) vs.emplace_back(a);
  for(Int b:bs) vs.emplace_back(b);
  vs.emplace_back(0);
  vs.emplace_back(1e9+6);

  vs=compress(vs);
  auto dc=dict(vs);
  Int sz=dc.size();

  const Int MOD = 1e9+7;
  using M = Mint<Int, MOD>;
  ArbitraryModConvolution arb;
  FormalPowerSeries<M> FPS([&](auto as,auto bs){return arb.multiply(as,bs);});

  using Poly = FormalPowerSeries<M>::Poly;

  Poly sum({1,1,500000004,333333336,208333335,933333340,384722225,953769848,884027784,28425375,878389832,120295265,667416506,229082322,168690037,792301837,189791907,537322580,270492550,482909819,434964639,603347984,256069033,40542057,910866921,438756389,689225591,456092267,413439436,942741942,190664686,782031312,604476028,573671381,838163729,26381583,992375502,930241799,68659206,750162938,475025082,44106509,953003110,354749308,929548052,773716788,337410579,936852063,239751572,561034786,757300345,866130835,553348107,173690227,339768055,709994974,599133150,808467741,396950722,936881852,933909478,737746550,781678380,976953545,580850150,325446247,537865815,281759879,678254613,501070706,851777585,443897119,629314534,760221421,466210161,508261591,65379122,70860701,553561602,854155236,407075847,92305888,282144425,99940577,300342438,587223921,290386237,874023958,985911658,291238936,785218916,678035252,407108295,192101397,507631876,885193819,934834163,385372845,417450165,966951672,684237800,52565350,530411501,135801688,482549358,210734100,761667073,954034475,693540720,576600855,148510276,919026764,583465058,956106104,181054957,41348431,224860616,517912143,860599260,727279538,906355640,153963332,118864415,34582699,44891509,32565076,105784827,928923967,903694428,235385416,883778964,689231689,547905546,909455137,465865460,662952760,195582959,432129855,680896262,758700879,501176266,776382822,454182726,365978689,459511347,816227295,999967985,931726294,294000060,267169976,42254724,349482774,808670797,253898299,508920118,703775403,785503876,423332329,660157859,247972241,450442033,165002242,361442380,392196376,978825741,920083817,560637228,355209713,832930192,440150331,375967478,305763913,635609914,188334856,10887821,335431951,444798249,529525353,226380424,33966925,136881343,434803890,922586534,569205127,117755704,850230335,9409131,93257910,499343559,777515079,650212468,412857608,653792744,679126849,627912655,420312949,612153221,845955439,166961824,673224688,890626117,315980351,994489857,197421005,255024280,293965643,551312195,954953948,756212493,145912941,421627841,799494402,930555555,355649848,186846433,48886853,726884935,842271550,621329810,400463499,99728277,259919265,910183168,345461687,647722720,465173355,355332005,670027204,429411872,891988152,9169256,451160948,499408796,131168601,198918642,129056918,498922473,98755571,915188909,895498700,154447049,565728210,321328855,10010840,606569580,973703597,842226469,741226137,421029601,247331280,864146768,199266677,950280814,999665342,469919529,13609624});
  /*
  const Int deg = 1<<8;
  {
    for(Int l=0;l<deg;l++){
      Poly res({M(1)});
      Poly bs({M(1),M(1)});
      bs=FPS.inv(bs,deg);
      Poly tmp({M(1)});
      for(Int i=1;i<=l;i++){
        tmp=FPS.pre(FPS.mul(tmp,bs),deg);
        res=FPS.pre(FPS.mul(res,FPS.sub(Poly({M(1)}),tmp)),deg);
      }
      sum=FPS.add(sum,res);
    }
    using E = Enumeration<M>;
    E::init(deg);
    for(Int i=0;i<deg;i++) cout<<sum[i]<<endl;
    for(Int i=0;i<deg;i++) sum[i]*=E::Finv(i);
    for(Int i=0;i<deg;i++) cout<<sum[i]<<",";
  }
  */

  vector< vector<M> > dp(n+1,vector<M>(sz,0));

  for(Int j=0;j+1<sz;j++)
    if(as[0]<=vs[j]&&vs[j+1]<=bs[0])
      dp[1][j]=M(vs[j+1]-vs[j])/M(bs[0]-as[0]);

  for(Int i=1;i<n;i++){
    M rev=M(bs[i]-as[i]).inv();
    vector< vector<M> > nx(n+1,vector<M>(sz,0));

    if(i&1){
      for(Int l=1;l<n;l++){
        for(Int j=0;j+1<sz;j++){
          nx[l+1][j]+=dp[l][j]*
            M(as[i]<=vs[j]&&vs[j+1]<=bs[i])*M(vs[j+1]-vs[j])*rev;

          for(Int k=j+1;k+1<sz;k++)
            nx[1][k]+=sum[l]*dp[l][j]
              *M(as[i]<=vs[k]&&vs[k+1]<=bs[i])*M(vs[k+1]-vs[k])*rev;
        }
      }
    }else{
      for(Int l=1;l<n;l++){
        for(Int j=0;j+1<sz;j++){
          nx[l+1][j]+=dp[l][j]*
            M(as[i]<=vs[j]&&vs[j+1]<=bs[i])*M(vs[j+1]-vs[j])*rev;

          for(Int k=j-1;k>=0;k--)
            nx[1][k]+=sum[l]*dp[l][j]
              *M(as[i]<=vs[k]&&vs[k+1]<=bs[i])*M(vs[k+1]-vs[k])*rev;
        }
      }
    }
    swap(dp,nx);
  }

  M ans{0};
  for(Int i=1;i<=n;i++)
    for(Int j=0;j+1<sz;j++)
      ans+=dp[i][j]*sum[i];

  cout<<ans<<endl;
  return 0;
}