#include<stdio.h>

#include<string.h.>

#define MAX 100001

int pie[MAX][];

int dp[MAX][];

int n;

int main()

{

    int i,j,time,location,maxtime,mid,left,right;

    while(scanf("%d",&n)!=EOF&&n){

        memset(pie,,sizeof(pie));

        memset(dp,,sizeof(dp));

        maxtime=;

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

            scanf("%d%d",&location,&time);

            pie[time][location+]++;

            if(time>maxtime)

                maxtime=time;

        }

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

            dp[maxtime][i]=pie[maxtime][i];

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

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

                left=dp[i+][j-]+pie[i][j];

                mid=dp[i+][j]+pie[i][j];

                right=dp[i+][j+]+pie[i][j];

                dp[i][j]=(left>mid)?left:mid;

                dp[i][j]=(dp[i][j]>right)?dp[i][j]:right;

            }

        }

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

    }

    return ;

}