#include <bits/stdc++.h>
using namespace std;
using ll = long long;
#define fi first
#define se second
const int maxn = 5e2+10;
const int MOD = (int)1e9+7;
pair<int,int> a[maxn];
unordered_map<int,int> dp[maxn];
int n;
int32_t main() {
cin >> n; int ans = 0;
for(int i = 0; i < n; i++) cin >> a[i].fi >> a[i].se;
for(int i = 0; i < n; i++){
for(int j = a[i].fi; j <= a[i].se; j++){
dp[i][j]=1;
if(j>a[i].fi) dp[i][j]+=dp[i][j-1];
if(dp[i][j]>MOD) dp[i][j]-=MOD;
for(int k = 0; k < i; k++){
if(j>a[k].fi) dp[i][j]+=dp[k][min(j-1,a[k].se)];
if(dp[i][j]>MOD) dp[i][j]-=MOD;
}
}
}
for(int i = 0; i < n; i++) ans+=dp[i][a[i].se], ans-=(ans>MOD?MOD:0);
cout << ans;
}
