#include<bits/stdc++.h>
using namespace std;
#define int long long
const int MOD = 1e9+7;
const int MAXV = 2000;
int put(int a, int exp)
{
if(exp==0)
return 1;
if(exp%2==0)
return put(a*a%MOD,exp/2);
else
return put(a*a%MOD,exp/2)*a%MOD;
}
int n,cate;
int le[505],ri[505];
map<int,int> mp,nrm;
int invnrm[MAXV+5],nr[MAXV+5];
int dp[MAXV+5][505];
int sumdp[MAXV+5];
int prec_inv[505];
signed main()
{
cin>>n;
for(int i=1;i<=n;i++)
{
cin>>le[i]>>ri[i];
mp[le[i]]++;
mp[ri[i]]++;
prec_inv[i] = put(i,MOD-2);
}
for(auto it:mp)
{
if(it.second)
{
nrm[it.first]=++cate;
invnrm[cate]=it.first;
cate++;
}
}
for(int i=1;i<=cate;i+=2)
{
nr[i]=1;
nr[i+1]=invnrm[i+2]-invnrm[i]-1;
}
dp[0][0]=1;
sumdp[0]=1;
for(int ult=1;ult<cate;ult++)
sumdp[ult] = sumdp[ult-1];
for(int i=1;i<=n;i++)
{
le[i] = nrm[le[i]];
ri[i] = nrm[ri[i]];
for(int ult=ri[i];ult>=le[i];ult--)
{
for(int cnt=min(i,nr[ult]);cnt>1;cnt--)
{
dp[ult][cnt]= (dp[ult][cnt] + dp[ult][cnt-1] * (nr[ult]-cnt+1)%MOD * prec_inv[cnt])%MOD;
}
dp[ult][1] = (dp[ult][1] + sumdp[ult-1]*nr[ult])%MOD;
}
sumdp[0]=1;
for(int ult=1;ult<cate;ult++)
{
sumdp[ult] = sumdp[ult-1];
for(int cnt=1;cnt<=i;cnt++)
sumdp[ult] = (sumdp[ult] + dp[ult][cnt])%MOD;
}
}
int rez=0;
for(int ult=1;ult<=cate;ult++)
for(int cnt=1;cnt<=n;cnt++)
rez = (rez + dp[ult][cnt])%MOD;
cout<<rez;
return 0;
}
