#include<iostream>

#include<cstdio>

#include<cstring>

#include<algorithm>

#include<cmath>

using namespace std;

int MAX(int a,int b)

{

    return a>b?a:b;

}

const int maxn = ;

int a[maxn][],n,dp[maxn][];

int main(void)

{

    int j,i,t,x;

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

    {

        memset(a,,sizeof(a));

        int mx=;

        for(i=;i<n;i++) scanf("%d%d",&x,&t),mx=MAX(mx,t),a[t][x]++;

        for(i=;i<=;i++) dp[mx][i]=a[mx][i];

        for(i=mx-;i>=;i--)

        {

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

            if(j==) dp[i][j]=a[i][j]+MAX(dp[i+][j],dp[i+][j+]);

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

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

        }

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

    }

    return ;

}