#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef vector<int> vi;
typedef vector<vi> vii;
typedef pair<int,int> pi;
typedef vector<pi> pii;
typedef tuple<int,int,int> tii;
typedef vector<ll> li;
typedef vector<li> lii;
#define REP(i,a,b) for(int i=a;i<b;i++)
#define F first
#define S second
#define PB push_back
#define MP make_pair
#define LSOne(s) ((s)&(-s))
ll INF=1e18+10;
int inf=1e9+10;
ll M=1e9+7;
int main() {
// ios::sync_with_stdio(0);
// cin.tie(0);
int n;cin>>n;
pii a(n);
REP(i,0,n)cin>>a[i].F>>a[i].S;
vector<ll> ans(n,0);
ans[0]=1;
REP(i,0,n){
int k=a[i].F;
if(k==0)continue;
REP(j,1,a[i].S+1){
if(i+j*k>=n)break;
ans[i+j*k]+=ans[i];
ans[i+j*k]%=M;
}
}
ll val=0;
REP(i,0,n){
val+=ans[i];
val%=M;
}
cout<<val;
}
