#include<stdio.h>

#include<string.h>

#include<algorithm>

#include<cmath>

#include<iostream>

using namespace std;

int dp[][];

int  main()

{

    int n;

    while(~scanf("%d",&n))

    {

        int x,t,maxs = -;

        if(n == ) break;

        memset(dp,,sizeof(dp));

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

        {

            scanf("%d%d",&x,&t);

            dp[x][t]++;

            if(t > maxs) maxs = t;

        }

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

        {

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

            {

                if(j == )

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

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

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

            }

        }

        printf("%d\n",dp[][]);

    }

}