#include<iostream>
#include<math.h>
using namespace std;
int main()
{
	int n,i,mintime=10000000,temp1,temp2,temp;
	while(scanf("%d",&n)&&n)
	{
		for(i=0;i<n;i++)
		{		
			scanf("%d%d",&temp1,&temp2);
			if(temp2<0)
			continue;
			temp=ceil((4.5/temp1)*3600)+temp2;
			if(temp<mintime)
			mintime=temp;
		}
		printf("%d\n",mintime);		
	}
	return 0;
	
}