#include <bits/stdc++.h>
using namespace std;
#define eps 1e6
int arr[100050],brr[100050];
double n,p;
bool check(double x){
	double sum=0;
	for(int i=1;i<=n;i++){
		if(brr[i]>=arr[i]*x) continue;
		sum+=arr[i]*x-brr[i];
	}
	return sum<=x*p;
}
int main(){
	cin>>n>>p;
	for(int i=1;i<=n;i++){
		cin>>arr[i];
		cin>>brr[i];
	}
	double r=1e10+100,l=1,ans=-1;
	while(r-l>eps){
		double mid=(r+l)/2;
		if(check(mid)){
			l=mid;
			ans=mid;
		}else{
			r=mid;
		}
	}
	if(ans==-1){
		cout<<-1;
		return 0;
	}
	printf("%.7lf",ans);
	return 0;
}

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