#include <bits/stdc++.h>
using namespace std;
#define ll long long
const ll DIM = 1e5 + 7;
const ll mod = 1e9 + 7;
ll dp[DIM];
int main(){
ios::sync_with_stdio(false);cin.tie(nullptr); cout.tie(nullptr);
ll n;
cin >> n;
dp[1] = 1;
for (int i=1; i<=n; i++) {
ll d, x;
cin >> d >> x;
if (d == 0) continue;
for (int j=i+d; j<=min(n, i + x*d); j++) {
dp[j] += dp[i];
dp[j] %= mod;
}
}
ll answer = 0;
for (int i=1; i<=n; i++) {
answer += dp[i];
answer %= mod;
}
cout << answer << endl;
}
;
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