#include<iostream>
#include<vector>
#include<algorithm>
using namespace std;
#define int long long
typedef pair<int,int> pii;
const int mod = 1e9+7;
int N;
vector<pii> range;
vector<int> des;
int f[503][503<<1];
signed main() {
cin>>N;
range.push_back({});
des.push_back(0);
for(int i=1; i<=N; i++) {
int L, R;
cin>>L>>R;
range.push_back({L, R+1}); // [L, R) => dp時比較好用
des.push_back(L);
des.push_back(R+1);
}
sort(des.begin()+1, des.end());
des.resize(unique(des.begin(), des.end()) - des.begin());
for(int i=1; i<=N; i++) {
range[i].first = lower_bound(des.begin()+1,des.end(), range[i].first) - des.begin();
range[i].second = lower_bound(des.begin()+1,des.end(), range[i].second) - des.begin();
}
int sz = des.size() - 1;
vector<int> l(sz);
for(int i=0; i<sz; i++) {
l[i] = des[i+1] - des[i];
}
vector<int> ni(N+1, 0);
ni[1] = 1;
for(int i=2; i<=N; i++) {
ni[i] = 1LL*(mod - mod / i) * ni[mod%i] % mod;
}
for(int i=0; i<sz; i++) f[0][i] = 1;
for(int i=1; i<=N; i++) {
for(int j = range[i].first, up = range[i].second; j < up; j++) {
int C = l[j], r = l[j], c = 1;
for(int k = i-1; k>=0; k--) {
(f[i][j] += 1LL*f[k][j-1]*C%mod)%=mod;
if(range[k].first <= j && j < range[k].second) {
r++; c++;
C = (1LL*C*r%mod)*ni[c]%mod; // C(r+1, c+1) = C(r, c) * (r+1) / (c+1)
}
}
}
for(int j=2; j<=sz; j++) (f[i][j] += f[i][j-1])%mod;
}
int ans = 0LL;
for(int i=1; i<=N; i++) {
(ans += f[i][sz])%mod;
}
cout<<ans;
}
