#include "bits/stdc++.h"
using namespace std;
#define N 500005
#define ll long long
const int M = 1e9 + 7;
ll n, a[N], b[N], ans;
map <pair<int,int>,int> dp;
int solve(int x,int mx) {
if(x == n + 1) {
return 1;
}
if(dp.find({x,mx})!=dp.end()) return dp[{x,mx}];
int var = solve(x + 1, mx);
for(int j = mx + 1; j <= b[x]; j++) {
var += solve(x + 1, j + 1);
var %= M;
}
dp[{x,mx}] = var;
return var;
}
int main () {
ios::sync_with_stdio(0);cin.tie(0);
cin >> n;
for(int i = 1; i <= n; i++) {
cin >> a[i] >> b[i];
}
cout << solve(1, 0);
}
