学步园

#include<stdio.h>

int main()
{

    int n;
    float sumf,sums,s,p;

    while(scanf("%d",&n)==1)
    {
        sumf=sums=0;
        while(n--)
        {
            scanf("%f%f",&s,&p);
            if(p!=-1)
            sums+=s;

            if(p>=90&&p<=100)
            sumf+=s*4;
            else if(p>=80)
            sumf+=s*3;
            else if(p>=70)
            sumf+=s*2;
            else if(p>=60)
            sumf+=s;

        }
       if(sums)
        printf("%.2f\n",sumf/sums);
        else
        printf("-1\n");
    }
    return 0;
}