#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], dp[100][1000001], ans, vis[100][1000001];
int solve(int x,int mx) {
if(x == n + 1) {
return 1;
}
// if(vis[x][mx]) 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;
}
// vis[x][mx] = 1;
// 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);
}
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