#include <iostream>
#include <algorithm>
#include <vector>
using namespace std;
const int mod = 1e9 + 7;
int n;
int st[1005], ed[1005], len[1005];
int inv[1005], dp[1005][1005];
vector<int> cc;
int add(int a, int b){
int res = a + b;
if(res >= mod) res -= mod;
return res;
}
int mul(int a, int b){
return (a * 1ll * b) % mod;
}
int main(){
ios_base::sync_with_stdio(0);
cin.tie(0); cout.tie(0);
cin >> n;
for(int i = 1; i <= n; i ++){
cin >> st[i] >> ed[i];
ed[i] ++;
}
inv[1] = 1;
for(int i = 2; i <= n; i ++)
inv[i] = mul(mod / i, mod - inv[mod % i]);
for(int i = 1; i <= n; i ++){
cc.push_back(st[i]);cc.push_back(ed[i]);
}
sort(cc.begin(), cc.end());
cc.erase(unique(cc.begin(), cc.end()), cc.end());
for(int i = 1; i <= n; i ++){
st[i] = upper_bound(cc.begin(), cc.end(), st[i]) - cc.begin();
ed[i] = upper_bound(cc.begin(), cc.end(), ed[i]) - cc.begin();
}
int sz = cc.size() - 1;
for(int i = 1; i <= sz; i ++)
len[i] = cc[i] - cc[i - 1];
dp[0][0] = 1;
for(int i = 1; i <= sz; i ++){
dp[i][0] = 1;
for(int j = 1; j <= n; j ++){
int choose = len[i]; int cnt = 1;
dp[i][j] = dp[i - 1][j];
if(i < st[j] || i >= ed[j]) continue;
for(int k = j - 1; k >= 0; k --){
dp[i][j] = add(dp[i][j], mul(dp[i - 1][k], choose));
if(st[k] <= i && i < ed[k]){
choose = mul(choose, mul(add(cnt, len[i]), inv[cnt + 1]));
cnt ++;
}
}
}
}
int ans = 0;
for(int i = 1; i <= n; i ++)
ans = add(ans, dp[sz][i]);
cout << ans << endl;
return 0;
}
