#include "iostream"
#include "string.h"
using namespace std;
int max(int a,int b){return a>b?a:b;}
int set[100010][12],dp[100010][16];int main(){int n,time,maxb,i,x,t,j;while(cin>>n){if(!n)break;time=0;maxb=0;memset(set,0,sizeof(set));for(i=1;i<=n;i++){cin>>x>>t;set[t][x]++;time=max(time,t);}for(i=0;i<=time;i++){for(j=0;j<=10;j++)dp[i][j]=0;}dp[0][5]=1;for(i=1;i<=time;i++){for(j=0;j<=10;j++){if(dp[i-1][j]){if(set[i][j-1]!=0&&j-1>=0)dp[i][j-1]=max(dp[i][j-1],dp[i-1][j]+set[i][j-1]);if(set[i][j]!=0)dp[i][j]=max(dp[i][j],dp[i-1][j]+set[i][j]);if(set[i][j+1]!=0&&j+1<=10)dp[i][j+1]=max(dp[i][j+1],dp[i-1][j]+set[i][j+1]);if(set[i][j-1]==0&&j-1>=0)dp[i][j-1]=max(dp[i][j-1],dp[i-1][j]+set[i][j-1]);if(set[i][j]==0)dp[i][j]=max(dp[i][j],dp[i-1][j]+set[i][j]);if(set[i][j+1]==0&&j+1<=10)dp[i][j+1]=max(dp[i][j+1],dp[i-1][j]+set[i][j+1]);}}//for(j=0;j<=10;j++)cout<<dp[i][j]<<' ';cout<<endl;
    }for(i=0;i<=10;i++){maxb=max(maxb,dp[time][i]);}if(maxb==0)cout<<0<<endl;else cout<<maxb-1<<endl;}
}

#include <iostream>
#include <string.h>
#include <stdio.h>
using namespace std;
int max3(int a,int b,int c)
{a = a>b?a:b;a = a>c?a:c;return a;
}
int max2(int a,int b)
{a = a>b?a:b;return a;
}
int t[100001][11];
int main()
{int n,T,x,max;while(scanf("%d",&n)&&n){memset(t,0,sizeof(t));max = 0;while(n--){scanf("%d %d",&x,&T);t[T][x]++;max = max>T?max:T;}for(int i = max-1; i >= 0; i--){for(int j = 0; j <= 10; j++){if(j==0)t[i][j] += max2(t[i+1][j],t[i+1][j+1]);else if(j==10) t[i][j] += max2(t[i+1][j],t[i+1][j-1]);else t[i][j] += max3(t[i+1][j-1],t[i+1][j],t[i+1][j+1]);}}cout<<t[0][5]<<endl;}return 0;
}