#include<iostream>
#include<math.h>
using namespace std;

int main()
{
	int n;
	double speed,offTime;
	double totalTime = 10000.0;
	double tempTime;
	cin>>n;
	while(n != 0)
	{
		while(n--)
		{
			cin>>speed>>offTime;
			if(offTime < 0)
				tempTime = 10000.0;
			else
				tempTime = ceil((4500.0*3.6)/speed)+offTime;
			if(tempTime < totalTime)
				totalTime = tempTime;
		}
		cout<<(int)totalTime<<endl;
		cin>>n;
	}
	return 0;
}