#include<stdio.h>
using namespace std;
bool light[2000010];
int n, t;
double a;
int main()
{
	scanf("%d", &n);
	for (int j = 1; j <= n; j++)
	{
	scanf("%lf%d", &a, &t);
	for (int i = 1; i <= t; t++)
	{
light[int(a * i)] = !light[int(a * i)];
		}
	}
	int k = 0;
	while (1)
	{
		if (light[k] == 1)
		{
			printf("%d", k);
			break;
		}
		k++;
	}
	return 0;
}