#include <bits/stdc++.h>
using namespace std;
#define ll long long
#define pb push_back
#define pii pair<int,int>
#define sz size()
#define all(v) v.begin(),v.end()
#define fi first
#define se second
const int N = 2e5;
const int mod = 998244353;
const int INF = 1e9;
const int di[] = {1, -1, 0, 0};
const int dj[] = {0, 0, 1, -1};
void solve() {
int n;
cin>>n;
int d[n+1],x[n+1];
for(int i = 1; i <= n; i++){
cin>>d[i]>>x[i];
}
int dp[n+1];
memset(dp,0,sizeof(dp));
dp[1]=1;
for(int i = 2; i <= n; i++){
for(int j = 1; j < i; j++){
if(d[j]==0)
continue;
if(i%d[j]==j%d[j] && (i-j)/d[j]<=x[j]){
dp[i]+=dp[j];
}
}
}
int ans=0;
for(int i = 1; i <= n; i++){
ans+=dp[i];
}
cout<<ans<<"\n";
}
int main() {
//freopen("cowrun.in","r",stdin);
//freopen("cowrun.out","w",stdout);
ios_base::sync_with_stdio(false);
cin.tie(nullptr);
cout.tie(nullptr);
int t=1;
//cin>>t;
while(t--) {
solve();
}
return 0;
}
