Losers always whine about their best. Winners go home and fuck the prom queen。

很操蛋却非常有意思的题目，注意变量的类型，学分能最后为0？分数的范围？很操蛋。

#include<iostream>

using namespace std;

void main()

{

	int n,temp=0;

	double cent,score=0,sum=0,count=0;

	while(cin>>n)

	{

		sum=0;count=0;

		for(int i=0;i<n;i++)

		{

			cin>>cent>>score;

			if(score!=-1)

			{

				count+=cent;

				if(score>=90)

					temp=4;

				else if(score>=80)

					temp=3;

				else if(score>=70)

					temp=2;

				else if(score>=60)

					temp=1;

				else if(score>=0)

					temp=0;

				sum+=cent*temp;

			}

		}

		 if(count==0)

			cout<<-1<<endl;

		else

			printf("%.2lf\n",sum/count);

	}

}