#include <bits/stdc++.h>
#define ST first
#define ND second
#define PB push_back
using namespace std;
using ll = long long;
using pi = pair<int,int>;
using vi = vector<int>;
const int nax = 500 + 10, mod = 1e9 + 7;
int n, mx;
map<int, int>dp, dp2;
int a[nax], b[nax];
int main() {
ios_base::sync_with_stdio(0);
cin.tie(0);
cin >> n;
for(int i = 1; i <= n; ++i) {
cin >> a[i] >> b[i];
}
dp[0] = 1;
for(int i = 1; i <= n; ++i) {
int sum = 0;
for(auto x : dp) sum = (sum + x.ND) % mod;
auto it = dp.end();
vector<pi>value = {};
for(int j = b[i]; j >= a[i]; --j) {
while(it != dp.begin() && (*prev(it)).ST >= j) {
it = prev(it);
sum = (sum - (*it).ND) % mod;
}
value.emplace_back(j, sum);
}
for(auto x : value) {
dp[x.ST] = (dp[x.ST] + x.ND) % mod;
}
}
int ans = 0;
for(auto x : dp) ans = (ans + x.ND) % mod;
ans--;
if(ans < 0) ans += mod;
cout << ans;
}
