#include <cstdio>
#include <stdio.h>
#include <stdbool.h>
#include <iostream>
#include <map>
#include <vector>
#include <climits>
#include <stack>
#include <string>
#include <queue>
#include <algorithm>
#include <set>
#include <unordered_set>
#include <unordered_map>
#include <cmath>
#include <cctype>
#include <bitset>
#include <iomanip>
#include <cstring>
#include <numeric>
#include <cassert>
using namespace std;
#define int long long
#define pii pair<int, int>
#define mp make_pair
#define pb push_back
#define fi first
#define se second
const int MOD = 1000000007;
int n;
vector<int> dp;
vector<pii> vect;
int train(int i){
if (i>=n)return 0;
if (dp[i]!=-1)return dp[i];
int res=1;
if (vect[i].fi)for (int j=1; j<=vect[i].se; ++j)res=(res+train(i+j*vect[i].fi))%MOD;
return dp[i]=res;
}
int32_t main(){
ios_base::sync_with_stdio(0);
cin.tie(0);
cout.tie(0);
cin>>n;
vect.resize(n);
dp.resize(n, -1);
for (int i=0; i<n; ++i)cin>>vect[i].fi>>vect[i].se;
cout<<train(0);
}
