/*
_.-- ,.--.
.' .' /
@ |'..--------._
/ \._/ '.
/ .-.- \
( / \ \
\\ '. | #
\\ \ -. /
:\ | )._____.' \
" | / \ | \ )
| |./' :__ \.-'
'--'
*/
#include<bits/stdc++.h>
#define ll long long
#define llll pair<ll,ll>
#define ii pair<int,int>
#define fi first
#define se second
#define FOR(i,l,r) for(int i=l;i<=r;i++)
#define FOD(i,r,l) for(int i=r;i>=l;i--)
#define ull unsigned long long
#define iii pair<int,ii>
#define iv pair<pii,ii>
#define db double
#define ld long double
#define pb push_back
#define tdk "kfph"
using namespace std;
const int dx[] = {1, -1, 0, 0};
const int dy[] = {0, 0, -1, 1};
const int dxx[] = {1, 1, -1, -1, 2, 2, -2, -2};
const int dyy[] = {2, -2, 2, -2, 1, -1, 1, -1};
const ll INF=1e18;
const int mod=1e9+7;
const int N=1e3+5;
int fact[N],inv[N],dp[N][N],a[N],b[N],n,m;
vector<int> val;
int add(int a,int b)
{
return (a+b)%mod;
}
int mul(int a,int b)
{
return 1ll*a*b%mod;
}
int sub(int a,int b)
{
return ((a-b)%mod+mod)%mod;
}
int binpow(int a,int b)
{
if(b==0) return 1;
int ans=binpow(a,b/2);
ans=mul(ans,ans);
if(b&1) return mul(ans,a);
return ans;
}
void kfph()
{
cin >> n;
fact[0]=1;
for(int i=1;i<=n;i++)
{
cin >> a[i] >> b[i];
val.pb(a[i]);
val.pb(b[i]+1);
fact[i]=mul(fact[i-1],i);
}
inv[n]=binpow(fact[n],mod-2);
for(int i=n-1;i>=0;i--)
{
inv[i]=mul(inv[i+1],i+1);
}
for(int i=1;i<=n;i++)
{
inv[i]=mul(inv[i],fact[i-1]);
}
val.pb(0);
sort(val.begin(),val.end());
val.erase(unique(val.begin(),val.end()),val.end());
m=val.size()-1;
for(int i=0;i<=n;i++)
{
dp[i][0]=1;
}
for(int j=1;j+1<=m;j++)
{
int numrange=val[j+1]-val[j];
for(int i=0;i<=n;i++)
{
dp[i][j]=dp[i][j-1];
int cnt=0;
int nck=1;
for(int k=i;k>=1;k--)
{
if(a[k]<=val[j] and val[j+1]<=b[k]+1)
{
cnt++;
nck=mul(nck,mul(inv[cnt],numrange+cnt-1));
dp[i][j]=add(dp[i][j],mul(dp[k-1][j-1],nck));
}
}
}
}
cout << sub(dp[n][m-1],1);
}
int main()
{
ios_base::sync_with_stdio(0);cin.tie(0);cout.tie(0);
if(fopen(tdk".inp","r"))
{
freopen(tdk".inp","r",stdin);
freopen(tdk".out","w",stdout);
}
int t=1;
//cin >> t;
while(t--)
{
kfph();
}
return 0;
}
