/*  This Code is Submitted by wywcgs for Problem 1716 on 2006-08-19 at 17:12:14 */ 
#include <cstdio>
#include <cmath>

const int N = 10240;
const double S = 4.5;

int main()
{
	int n, v[N], t[N];
	
	while(scanf("%d", &n) != EOF && n != 0) {
		for(int i = 0; i < n; i++) scanf("%d %d", &v[i], &t[i]);
		double rt = 1e20;
		for(int i = 0; i < n; i++) {
			if(t[i] < 0) continue;
			rt <?= S*3600/v[i]+t[i];
		}
		printf("%.0lf\n", ceil(rt));
	}
	
	return 0;
}