#include <bits/stdc++.h>
using namespace std;
#define N 510
#define ll long long
#define fs first
#define sc second
#define ii pair<ll,int>
#define pb push_back
#define int ll
const ll mod=1e9+7;
void selfadd(int&u,int v)
{
u+=v;
if(u>=mod)u-=mod;
// u=(u+v)%mod;
}
int n,l[N],r[N];
vector<int>dp[N];
int32_t main()
{
#ifdef SKY
freopen("A.inp","r",stdin);
freopen("A.out","w",stdout);
#endif // SKY
ios::sync_with_stdio(0);
cin.tie(NULL);
cout.tie(NULL);
cin>>n;
for(int i=1;i<=n;i++)
{
cin>>l[i]>>r[i];
dp[i].resize(r[i]-l[i]+1,0);
}
for(int i=1;i<=n;i++)
for(int j=l[i];j<=r[i];j++)
{
dp[i][j-l[i]]=1;
if(j>l[i])
dp[i][j-l[i]]=dp[i][j-l[i]-1]+1;
// cout<<i<<" "<<j<<" "<<dp[i][j-l[i]]<<endl;
for(int k=1;k<i;k++)
{
if(j>r[k])
{
selfadd(dp[i][j-l[i]],dp[k].back());
continue;
}
if(j<=l[k])
continue;
selfadd(dp[i][j-l[i]],dp[k][j-l[k]-1]);
}
// cout<<i<<" "<<j<<" "<<dp[i][j-l[i]]<<endl;
}
int res=0;
for(int i=1;i<=n;i++)
selfadd(res,dp[i].back());
cout<<(res+mod*mod)%mod;
return 0;
}
