#include<bits/stdc++.h>
using namespace std;
int n,p,a[100005],b[100005],zhong=0;
bool check(double m)
{
	double sum=0;
	for(int i=1;i<=n;++i)
	{
		sum+=min(0.0,b[i]-a[i]*m);
	}
	return sum<=p*m;
}
int main()
{
	scanf("%d %d",&n,&p);
	for(int i=1;i<=n;++i)
	{
		scanf("%d %d",&a[i],&b[i]);
		zhong+=a[i];
	}
	if(zhong<=p)
	{
		printf("-1\n");
		return 0;
	}
	double l=0,r=1e7,mid,ans;
	while(r-l>1e-11)
	{
		mid=(l+r)/2;
		if(check(mid))
		{
			ans=mid;
			r=mid;
		}
		else
		{
			l=mid;
		}
	}
	printf("%.10f",ans);
    return 0;
}