#include <iostream>
#include <cstdio>
#include <cstring>
#include <cstdlib>
#include <algorithm>

using namespace std;

int dp[100005][15];

int main()
{
    int n, x, t;
    while(scanf("%d",&n),n)
    {
        memset(dp, 0, sizeof(dp));
        for(int i=1; i<=n; i++)
        {
            scanf("%d %d", &x, &t);
            dp[t][x+1] += 1;
        }

        for(int i=100000; i>=0; i--)
        {
            for(int j=1; j<=11; j++)
            {
                dp[i][j] += max(dp[i+1][j],max(dp[i+1][j+1],dp[i+1][j-1]));
            }
        }

        printf("%d\n",dp[0][6]);
    }

    return 0;
}