#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
const ll mod=1e9+7;
ll n,c[1001],st[501],ed[501],cnt,comb[501];
ll dp[501][1001];
set<int> ss;
ll power(ll a, ll m) { //a^m;
ll ans=1;
while (m) {
if (m%2==1) ans=(ans*a)%mod;
a=(a*a)%mod;
m/=2;
}
return ans;
}
int main() {
ios_base::sync_with_stdio(0); cin.tie(0);
cin>>n;
for (int i=1; i<=n; ++i) {
cin>>st[i]>>ed[i]; --st[i];
ss.insert(st[i]);
ss.insert(ed[i]);
}
for (int i=1; i<=n; ++i) comb[i]=power(i,mod-2)%mod;
cnt=ss.size()-1;
int id=0;
for (auto it=ss.begin(); it!=ss.end(); ++it) c[id++]=*it;
for (int i=0; i<=cnt; ++i) dp[0][i]=1;
for (int i=1; i<=n; ++i) {
dp[i][0]=1; //don't send any boat
for (int j=1; j<=cnt; ++j) { //consider from the range from c[j-1]+1 to c[j]
dp[i][j]=dp[i][j-1];
ll idx=1,com=1;
for (auto k=i; k>0; --k) {
if (st[k]<c[j] && c[j]<=ed[k]) {
com=((com*(c[j]-c[j-1]+idx-1)%mod)*comb[idx])%mod;
dp[i][j]=(dp[i][j]+dp[k-1][j-1]*com)%mod;
++idx;
}
}
}
}
cout<<(dp[n][cnt]-1+mod)%mod;
}
