/*
* Author: Geunwoo Bae(functionx)
* Time Complexity: O(N^2 lg N)
*/
#include<stdio.h>
#include<cmath>
#include<complex>
#include<algorithm>
#include<vector>
#define mod 1000000007
using namespace std;
typedef long long lld;
typedef complex<double> base;
struct qry {
int ix;
lld x, pm;
bool operator< (const qry& c) const {
return x<c.x;
}
}que[11010];
int n, chk[5050], act, qcn;
lld dy[5050], inv[5050];
void fft(vector <base> &a, bool invert){
int n = a.size();
for(int i=1,j=0; i<n; i++){
int bit = n>>1;
for(; j>=bit; bit>>=1)j -= bit;
j += bit;
if(i<j)swap(a[i], a[j]);
}
for(int len=2; len<=n; len<<=1){
double ang = 2*M_PI/len*(invert?-1:1);
base wlen(cos(ang), sin(ang));
for(int i=0; i<n; i+=len){
base w(1);
for(int j=0; j<len/2; j++){
base u=a[i+j], v=a[i+j+len/2]*w;
a[i+j] = u+v;
a[i+j+len/2] = u-v;
w *= wlen;
}
}
}
if(invert){
for(int i=0; i<n; i++)a[i] /= n;
}
}
void convolution(vector<lld>& x, vector<lld>& y, const int sz){
vector<base> fa1, fa2, fb1, fb2;
int n, i;
for(n=1; n<sz; n<<=1);
for(i=0; i<n; i++){
fa1.push_back(0), fa2.push_back(0);
fb1.push_back(0), fb2.push_back(0);
}
for(i=0; i<sz; i++){
fa1.push_back(x[i]/30000), fa2.push_back(x[i]%30000);
fb1.push_back(y[i]/30000), fb2.push_back(y[i]%30000);
}
n<<=1;
fa1.resize(n), fa2.resize(n);
fb1.resize(n), fb2.resize(n);
fft(fa1, 0), fft(fa2, 0);
fft(fb1, 0), fft(fb2, 0);
for(i=0; i<n; i++){
base a1b1 = fa1[i]*fb1[i], a1b2 = fa1[i]*fb2[i];
base a2b1 = fa2[i]*fb1[i], a2b2 = fa2[i]*fb2[i];
fa1[i] = a1b1, fa2[i] = a1b2, fb1[i] = a2b1, fb2[i] = a2b2;
}
fft(fa1, 1), fft(fa2, 1);
fft(fb1, 1), fft(fb2, 1);
for(i=0; i<sz; i++){
lld a1b1, a1b2, a2b1, a2b2;
a1b1 = lld(fa1[i].real() + (fa1[i].real()>0 ? 0.5:-0.5)), a1b1%=mod;
a1b2 = lld(fa2[i].real() + (fa2[i].real()>0 ? 0.5:-0.5)), a1b2%=mod;
a2b1 = lld(fb1[i].real() + (fb1[i].real()>0 ? 0.5:-0.5)), a2b1%=mod;
a2b2 = lld(fb2[i].real() + (fb2[i].real()>0 ? 0.5:-0.5)), a2b2%=mod;
x[i] = (a1b1*900000000ll + (a1b2+a2b1)*30000ll + a2b2)%mod;
}
}
/*
void convolution(vector<lld>& x, vector<lld>& y, const int sz){
int i, j;
for(i=sz-1; i>=0; i--){
lld sum=0;
for(j=0; j<=i; j++){
sum+=x[j]*y[i-j];
sum%=mod;
}
x[i]=sum;
}
}*/
lld pw(lld a, lld b){
if(b<=0)return 1;
lld g=pw(a,b/2);
g=(g*g)%mod;
if(b%2)g=(g*a)%mod;
return g;
}
int main(){
int i;
lld pv;
scanf("%d", &n);
for(i=0; i<n; i++){
lld s, e;
scanf("%lld%lld", &s, &e);
que[qcn].ix=i, que[qcn].x=s, que[qcn++].pm=1;
que[qcn].ix=i, que[qcn].x=e+1, que[qcn++].pm=-1;
}
for(i=1; i<=n; i++)inv[i]=pw(i, mod-2);
sort(que, que+qcn);
pv=0;
for(i=0; i<qcn; i++){
if(pv<que[i].x && act){
lld psum=-1, sum=0, mul=1;
int j, ccn=0;
vector <lld> p, q;
for(j=0; j<n; j++){
if(chk[j]){
lld arg = sum-psum+mod;
while(arg>=mod)arg-=mod;
mul *= (que[i].x-pv+ccn)*inv[ccn+1]%mod;
mul %= mod;
p.push_back(arg);
q.push_back(mul);
psum=sum;
ccn++;
}
sum += dy[j];
if(sum >= mod)sum -= mod;
}
convolution(p, q, ccn);
for(j=ccn=0; j<n; j++){
if(chk[j]){
dy[j] += p[ccn];
if(dy[j] >= mod)dy[j] -= mod;
ccn++;
}
}
}
/* printf("%lld ~ %lld:\n", pv, que[i].x-1);
for(int j=0; j<n; j++)printf("%lld ", dy[j]);
puts("");*/
pv = que[i].x;
chk[que[i].ix] += que[i].pm, act += que[i].pm;
}
lld sum=0;
for(i=0; i<n; i++){
sum += dy[i];
if(sum >= mod)sum -= mod;
}
printf("%lld", sum);
return 0;
}
