#pragma GCC optimize("O3")
#include <bits/stdc++.h>
#define ll long long
#define str string
#define pb push_back
#define pf push_front
#define in insert
#define all(v) v.begin(),v.end()
const int sz=1000000,INF=1000000000,MOD=1000000007;
using namespace std;
void solve()
{
ll n,num1,num2,ans=0;
cin>>n;
vector<pair<ll,ll>>nums;
vector<map<ll,ll>>dp(n+1);
for(int i=0;i<n;i++)
{
cin>>num1>>num2;
nums.pb({num1,num2});
}
dp[1][0]=1;
for(int i=nums[0].first;i<=nums[0].second;i++)
{
dp[1][i]=1;
}
for(int i=2;i<=n;i++)
{
for(auto Dp:dp[i-1])
{
dp[i][0]=(dp[i][0]+Dp.second)%MOD;
}
for(auto Dp:dp[i-1])
{
for(int j=nums[i-1].first;j<=nums[i-1].second;j++)
{
if(Dp.first<j)
{
dp[i][j]=(dp[i][j]+Dp.second)%MOD;
}
}
}
}
for(auto Dp:dp[n])
{
ans=(ans+Dp.second)%MOD;
}
cout<<ans-1;
}
int main()
{
ios_base::sync_with_stdio(false);
cin.tie(nullptr),cout.tie(nullptr);
ll t=1;
//cin>>t;
while(t--)
{
solve();
}
}
