#include <bits/stdc++.h>
using namespace std;
#define ll long long
#define vi vector<ll>
#define vvi vector<vi>
#define pp pair<ll, ll>
#define vp vector<pp>
#define inf 1000000000
#define mod 1000000007
int main(){
cin.tie(0);
ios_base::sync_with_stdio(false);
ll n;
cin >> n;
vp A(n);
for(int i = 0; i < n; i++){
cin >> A[i].first >> A[i].second;
}
ll k = 200;
ll ANS = 0;
vi ans(n, 0);
ans[0] = 1;
for(int i = 0; i < n; i++){
ANS += ans[i];
ANS %= mod;
if(A[i].first == 0) continue;
for(int j = 1; j <= A[i].second; j++){
ll pos = i + j * A[i].first;
if(pos >= n) break;
ans[pos] += ans[i];
ans[pos] %= mod;
}
}
cout << ANS << '\n';
}
