#include<stdio.h>
#include<string.h>
int max(int a,int b)
{
return a>b?a:b;
}
int bei[12][100003];
int main()
{
int m,i,j;
//freopen("in.txt","r",stdin);
while( scanf("%d",&m)&&m)
{
int a,b,T=0;
memset(bei,0,sizeof(bei));
while(m--)
{
scanf("%d%d",&a,&b);
bei[a][b]++; //时间为b,,位移为a;
T<b?T=b:b; //选出最大时间;
}
for(j=0; j<11; j++)
for(i=T-1; i>=0; i--)
{
if(j==0)
bei[j][i]+=max(bei[ j+1][i],bei[j+1][i+1]);
else
bei[j][i]+=max(max(bei[j+1][i],bei[j+1][i+1]),bei[j+1][i-1]);
}
printf("%d\n",bei[5][0]);
}
return 0;
}