#include <stdio.h>
int main()
{
	long n,time=-1,v,i,t;
	double q;
	scanf("%d",&n);
	while (n!=0)
	{
		for (i=0;i<n;i++)
		{
			scanf("%d%d",&v,&t);
			if (t>=0)
			{
				q=ceil(t+4.5*3600.0/v);
				if ((time>q)||(time==-1))
					time=q;
			}
				
		}
		printf("%d\n",time);
		scanf("%d",&n);
		time=-1;
	}
	return 0;	
}