纯模拟，甚至用std::cin都不会超时

#include <cstdio>
#include <algorithm>
#include <cmath>

int f[2000010], n;

int main()
	for(int i = 0; i <= 2000000; i = i + 1)
	{
		f[i] = -1;
	}//初始化
	std::cin >> n;
	for(int i = 1; i <= n; i ++)
	{
		double a, t;
		std::cin >> a >> t;
		for(double i = 1; i <= t; i = i + 1)
		{
			f[int(a * i)] = f[int(a * i)] * -1;//每一个满足条件的灯改变状态
		
	}
	for(int i = 1; i <= 2000000; i ++)
	{
		if(f[i] == 1)
		{
			std::cout << i;
			return 0;//找到就结束，不用再找了
		}
	}
	return 0; 
}