#include<cstdio>

#include<cstring>

#include<algorithm>

#include<cstdlib>

#include<iostream>

#include<cmath>

using namespace std;

typedef long long ll;

int dp[][];

int main(){

    ios::sync_with_stdio();

    int n,x,t;

    while(cin>>n&&n){

        memset(dp,,sizeof dp);

        for(int i=;i<n;i++){

            cin>>x>>t;

            dp[t][x+]++;

        }

        for(int i=-;i>=;i--){

            for(int j=;j<=;j++){

                dp[i][j]+=max(dp[i+][j],max(dp[i+][j-],dp[i+][j+]));

            }

        }

        cout<<dp[][]<<"\n";

    }

    return ;

}