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//Asimple
#include<iostream>
#include<cstring>
using namespace std;
int maxi(int a,int b,int c)
{
    int max1;
    max1=a>b?a:b;
    max1=max1>c?max1:c;
    return max1;
}
int c[100001][11];
int main()
{
    int i,j;
    int n,a,b;
    while(cin>>n&&n)
    {
        int m=0;
        memset(c,0,sizeof(c));
        for(i=0;i<n;i++)
        {
             cin>>a>>b;
             c[b][a]++;
             if(m<b)
             m=b;
        }
        for(i=m-1;i>=0;i--)
        {
            for(j=1;j<=9;j++)
                c[i][j]+=maxi(c[i+1][j-1],c[i+1][j],c[i+1][j+1]);
            c[i][0]+=max(c[i+1][0],c[i+1][1]);
            c[i][10]+=max(c[i+1][10],c[i+1][9]);
        }
        cout<<c[0][5]<<endl;       
    }
    return 0;
}