#include <bits/stdc++.h>
//#define int long long
#define F first
#define S second
#define pb push_back
#define B begin()
#define E end()
using namespace std;
int n;
int a[1000];
int b[1000];
map<pair<pair<int,int>,int>,int>dp;
//map<pair<pair<int,int>,int>,int>go;
const int mod=1e9+7;
//dp[ { {i,last},pl } ]
int T;
long long f(int i,int last,int pl)
{
if(dp[ { {i,last},pl } ]!=0)
return dp[ { {i,last},pl } ]%mod;
T++;
if(i==n+1)
return 1;
long long g=f(i+1,last,pl);
for(int j=a[i];j<=b[i];j++)
if(j>a[last]+pl)
g+=f(i+1,i,j-a[i]);
//cout<<" "<<i<<" "<<last<<" "<<pl<<endl;
//go[ { {i,last},pl } ]=1;
return dp[ { {i,last},pl } ]=g%mod;
}
signed main()
{
T=0;
ios_base::sync_with_stdio(0);
cin.tie(0);
cout.tie(0);
//memset(dp,-1,sizeof dp);
cin>>n;
for(int i=1;i<=n;i++){
//a[i]=n-i;
cin>>a[i]>>b[i];
}
cout<<f(1,0,0)-1<<endl;
// cout<<T<<endl;
}
