#include <bits/stdc++.h>
#define int long long
using namespace std;
const int N=510, Mod=1e9+7;
int n, m, a[N], b[N], f[N], fi[N], s[2*N][N], x[N][2*N];
vector<int> c;
int Pow(int a, int b) {
if(!b) return 1;
int tmp=Pow(a, b/2); tmp=(tmp*tmp)%Mod;
if(b&1) tmp=(tmp*a)%Mod;
return tmp;
}
signed main() {
ios_base::sync_with_stdio(0); cin.tie(0);
f[0]=fi[0]=1;
for(int i=1; i<N; i++) f[i]=(f[i-1]*i)%Mod, fi[i]=(fi[i-1]*Pow(i, Mod-2))%Mod;
cin>>n;
for(int i=1; i<=n; i++) {
cin>>a[i]>>b[i];
c.push_back(a[i]), c.push_back(b[i]+1);
}
c.push_back(0), c.push_back(1);
sort(c.begin(), c.end()), c.erase(unique(c.begin(), c.end()), c.end());
m=c.size()-1;
for(int i=1; i<=m; i++) {
x[0][i]=1, s[i][1]=c[i]-c[i-1];
for(int j=2; j<=n; j++) {
s[i][j]=1;
for(int k=0; k<j; k++) s[i][j]=(s[i][j]*(s[i][1]-k))%Mod;
s[i][j]=(s[i][j]*fi[j])%Mod;
}
}
for(int i=1; i<=n; i++) {
for(int j=1; j<=m; j++) {
x[i][j]=(x[i][j-1]+x[i-1][j]-x[i-1][j-1]+Mod)%Mod;
if(a[i]<=c[j-1] && c[j]-1<=b[i]) {
for(int k=i-1; k>=0; k--) x[i][j]=(x[i][j]+s[i][i-k]*x[k][j-1])%Mod;
}
}
}
cout<<(x[n][m]+Mod-1)%Mod;
return 0;
}
