#include<stdio.h>
#include<string.h>

#define N 110000
#define max(a,b) (a>b?a:b)
#define max3(a,b,c) (max(a,max(b,c)))

int dp[N][20];

int main()
{
    int n;

    while(scanf("%d", &n), n)
    {
        int Max=0, time, p, i, j;

        memset(dp, 0, sizeof(dp));

        for(i=0; i<n; i++)
        {
            scanf("%d%d", &p, &time);
            Max = max(Max, time);
            dp[time][p+1]++;
        }

        for(i=Max-1; i>=0; i--)
        for(j=1; j<=11; j++)
        {
            dp[i][j] += max3(dp[i+1][j-1], dp[i+1][j], dp[i+1][j+1]);
        }

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

    return 0;
}