#include <bits/stdc++.h>
using namespace std;
#define int long long
const int sz = 2e5+5;
const int mod = 1e9+7;
int dp[sz];
signed main(){
ios::sync_with_stdio(false);
cin.tie(nullptr);
int n;
cin >> n;
vector<array<int, 2>> v;
for(int i = 0; i < n; i++){
int a, b;
cin >> a >> b;
v.push_back({a, b});
}dp[1] = 1;
for(int i = 1; i <= n; i++){
if(v[i-1][0] == 0) continue;
for(int j = 1; j <= v[i-1][1]; j++){
if(i + j*v[i-1][0] > n) break;
dp[i + j*v[i-1][0]] = (dp[i + j*v[i-1][0]] + dp[i]) % mod;
}
}int s = 0;
for(int i = 1; i <= n; i++){
s += dp[i];
s%=mod;
}cout << s << endl;
}
