#include <bits/stdc++.h>
using namespace std;
#define int long long
const int SQRT = 0;
int32_t main(int32_t argc,char* argv[]){
ios_base::sync_with_stdio(false);
cin.tie(nullptr);
int N;
cin >> N;
vector<int> d(N+1);
vector<int> x(N+1);
for(int i=1;i<=N;i++){
cin >> d[i] >> x[i];
}
vector<int> DP(N+1);
vector prefix(N+1,vector<int>(SQRT+1));
DP[1]++;
int ans = 0;
for(int i=1;i<=N;i++){
for(int j=1;j<=SQRT;j++){
if(i-j<0)continue;
prefix[i][j]+=prefix[i-j][j];
DP[i]+=prefix[i][j];
}
ans+=DP[i];
if(d[i]<=SQRT){
prefix[i][d[i]]+=DP[i];
if(i+(x[i]+1ll)*d[i]<=N)prefix[i+(x[i]+1ll)*d[i]][d[i]]-=DP[i];
} else {
for(int j=1;j<=x[i];j++){
if(j*d[i]+i>N)break;
DP[j*d[i]+i]+=DP[i];
}
}
}
cout << ans << '\n';
}
