#include <bits/stdc++.h>
using namespace std;
#define ll long long
const int nx=505, mod=1e9+7;
ll n, a[nx], b[nx], dp[nx][2*nx], qs[nx][2*nx], sz[2*nx], t, pv, ncr[nx][nx], choose[2*nx][nx], l[nx], r[nx];
map<ll, ll> mp;
ll invmod(ll a, ll x)
{
if (x==0) return 1;
auto tmp=invmod(a, x/2);
tmp=(tmp*tmp)%mod;
if (x%2) return (tmp*a)%mod;
else return tmp;
}
int main()
{
cin.tie(NULL)->sync_with_stdio(false);
cin>>n;
mp[0]=0;
for (int i=1; i<=n; i++) cin>>a[i]>>b[i], mp[--a[i]]=0, mp[b[i]]=0;
for (auto &[x, y]:mp) y=t, sz[t]=x-pv, pv=x, t++;
for (int i=1; i<=n; i++) l[i]=mp[a[i]], r[i]=mp[b[i]];
ncr[0][0]=1;
for (int i=1; i<=n; i++)
{
for (int j=0; j<=i; j++)
{
ncr[i][j]=ncr[i-1][j];
if (j>0) ncr[i][j]=(ncr[i][j]+ncr[i-1][j-1])%mod;
}
}
for (int i=1; i<t; i++)
{
//cout<<"sz "<<i<<' '<<sz[i]<<'\n';
ll tmp=1;
choose[i][0]=tmp;
for (int j=1; j<=min(sz[i], n); j++) tmp=(((tmp*(sz[i]-j+1))%mod)*invmod(j, mod-2))%mod, choose[i][j]=tmp;
}
for (int i=1; i<=n; i++)
{
//cout<<"l "<<i<<' '<<l[i]<<' '<<r[i]<<'\n';
for (int j=1; j<t; j++)
{
if (l[i]<j&&j<=r[i])
{
dp[i][j]=((qs[i-1][j-1]+1)*sz[j])%mod;
ll cnt=1;
for (int k=i-1; k>=1; k--)
{
if (l[k]<j&&j<=r[k]) cnt++;
if (cnt>=2)
{
ll sm=0;
for (int tmp=0; tmp<=cnt-2; tmp++) sm=(sm+choose[j][cnt]*ncr[cnt-2][tmp])%mod;
dp[i][j]=(dp[i][j]+sm*(qs[k-1][j-1]+1))%mod;
}
}
}
//cout<<"dp "<<i<<' '<<j<<' '<<dp[i][j]<<'\n';
qs[i][j]=((dp[i][j]+qs[i-1][j]+qs[i][j-1]-qs[i-1][j-1])%mod+mod)%mod;
}
}
cout<<qs[n][t-1];
}
