#include <bits/stdc++.h>
using namespace std;
using i64 = int64_t;
int mod = 1'000'000'007;
vector<int> parents[10000];
int dp[10000];
int main() {
cin.tie(0);
cout.tie(0);
ios_base::sync_with_stdio(false);
int N; cin >> N;
for (int i = 0; i < N; ++i) {
int d, x;
cin >> d >> x;
if (d == 0) continue;
for (int j = i + d; j < N && j <= i + d * x; ++j) {
parents[j].emplace_back(i);
}
}
memset(dp, 0, sizeof(dp));
int sum = dp[0] = 1;
for (int i = 1; i < N; ++i) {
for (int parent : parents[i]) {
dp[i] = (dp[i] + dp[parent]) % mod;
}
sum = (sum + dp[i]) % mod;
}
cout << sum;
}
