#include<bits/stdc++.h>
using namespace std;
double a[100008],b[100008];double sum;
double n,p;
double eps=1e-7;
bool check(double x){
	double t=x*p;
	double sum=0;
	for(int i=1;i<=n;i++){
		if(a[i]*x<=b[i]){
			continue;
		}else{
			sum+=(a[i]*x-b[i]);
		}
	}
	return sum<=t;
}
int main(){
	cin>>n>>p;
	for(int i=1;i<=n;i++){
		scanf("%lf",&a[i]);
		scanf("%lf",&b[i]);
		sum+=a[i];
	}
	if(sum<=p){
		cout<<-1;
		return 0;
	}
	double l=0;double r=1e10;
	while(r-l>eps){
		double mid=(l+r)/2;
		if(check(mid)){
			l=mid;
		}else{
			r=mid;
		}
	}
	printf("%.6f",l);
	
	return 0;
}