#define _USE_MATH_DEFINES
#include <bits/stdc++.h>
using namespace std;
//template
#define rep(i,a,b) for(int i=(int)(a);i<(int)(b);i++)
#define ALL(v) (v).begin(),(v).end()
typedef long long int ll;
const int inf = 0x3fffffff; const ll INF = 0x1fffffffffffffff; const double eps=1e-12;
template<typename T>inline bool chmax(T& a,T b){if(a<b){a=b;return 1;}return 0;}
template<typename T>inline bool chmin(T& a,T b){if(a>b){a=b;return 1;}return 0;}
//end
template<unsigned mod=1000000007>struct fp {
int v; static unsigned get_mod(){return mod;}
int inv() const{
int tmp,a=v,b=mod,x=1,y=0;
while(b)tmp=a/b,a-=tmp*b,swap(a,b),x-=tmp*y,swap(x,y);
if(x<0){x+=mod;} return x;
}
fp():v(0){}
fp(ll x):v(x>=0?x%mod:mod+(x%mod)){}
fp operator-()const{return fp(-v);}
fp pow(ll t){fp res=1,b=*this; while(t){if(t&1)res*=b;b*=b;t>>=1;} return res;}
fp& operator+=(const fp& x){if((v+=x.v)>=(int)mod)v-=mod; return *this;}
fp& operator-=(const fp& x){if((v+=mod-x.v)>=(int)mod)v-=mod; return *this;}
fp& operator*=(const fp& x){v=ll(v)*x.v%mod; return *this;}
fp& operator/=(const fp& x){v=ll(v)*x.inv()%mod; return *this;}
fp operator+(const fp& x)const{return fp(*this)+=x;}
fp operator-(const fp& x)const{return fp(*this)-=x;}
fp operator*(const fp& x)const{return fp(*this)*=x;}
fp operator/(const fp& x)const{return fp(*this)/=x;}
bool operator==(const fp& x)const{return v==x.v;}
bool operator!=(const fp& x)const{return v!=x.v;}
}; using Fp=fp<>;
template<typename T>struct factorial {
vector<T> Fact,Finv,Inv;
factorial(int maxx){
Fact.resize(maxx); Finv.resize(maxx); Inv.resize(maxx);
Fact[0]=Fact[1]=Finv[0]=Finv[1]=Inv[1]=1;
rep(i,2,maxx){Fact[i]=Fact[i-1]*i;} Finv[maxx-1]=Fact[maxx-1].inv();
for(int i=maxx-1;i>=2;i--){Finv[i-1]=Finv[i]*i; Inv[i]=Finv[i]*Fact[i-1];}
}
T fact(int n,bool inv=0){if(inv)return Finv[n];else return Fact[n];}
T inv(int n){return Inv[n];}
T nPr(int n,int r){if(n<0||n<r||r<0)return Fp(0);else return Fact[n]*Finv[n-r];}
T nCr(int n,int r){if(n<0||n<r||r<0)return Fp(0);else return Fact[n]*Finv[r]*Finv[n-r];}
};
Fp dp[510][1010],c[1010][510]; factorial<Fp> fact(1010);
int main(){
int n; cin>>n;
vector<int> a(n),b(n),vs={0,inf};
rep(i,0,n){
cin>>a[i]>>b[i]; b[i]++;
vs.push_back(a[i]);
vs.push_back(b[i]);
}
sort(ALL(vs)); vs.erase(unique(ALL(vs)),vs.end());
int m=vs.size();
rep(i,0,n){
a[i]=lower_bound(ALL(vs),a[i])-vs.begin();
b[i]=lower_bound(ALL(vs),b[i])-vs.begin();
}
//precalc
rep(i,0,m-1){
c[i][0]=1;
rep(j,0,n)c[i][j+1]=c[i][j]*(vs[i+1]-vs[i]+j)*fact.inv(j+1);
}
Fp res;
rep(i,0,n){
rep(j,a[i],b[i]){
int cnt=0;
for(int k=i;k;k--){
if(a[k]<=j and j<b[k])cnt++;
dp[i][j+1]+=dp[k-1][j]*c[j][cnt];
}
if(a[0]<=j and j<b[0])cnt++;
dp[i][j+1]+=c[j][cnt];
}
rep(j,0,m-1)dp[i][j+1]+=dp[i][j];
res+=dp[i][m-1];
}
cout<<res.v<<endl;
return 0;
}
