代码：

#include <iostream>
#include <cmath>
using namespace std;

int main()
{
	int n;
	bool light[2000002] = {0};
	cin >> n;
	while (n--)
	{
		int t;
		double a;
		cin >> a >> t;
		for (int i = 1; i <= t; i++)
			light[int(floor(a) * i)] = !light[int(floor(a) * i)];  // 反向操作一次
	}
	for (int i = 1;i <= 2000000; i++)  // 遍历寻找开着的灯
	{
		if (light[i] == 1)
		{
			cout << i << endl;
			break;
		}
	}
	
	return 0;
}