#include<bits/stdc++.h>
using namespace std;
int n,p,a[114514],b[114514];
long long sum1,sum2;
long double l,r=1e10;
bool check(long double x){
	long double sum=0;
	for(int i=1;i<=n;i++){
		if(x*a[i]>b[i])sum+=x*a[i]-b[i];
	}
	return sum>=x*p; 
}
int main(){
	cin>>n>>p;
	for(int i=1;i<=n;i++){
		cin>>a[i]>>b[i];
		sum1+=a[i];
	}	
	if(sum1>=p){
		cout<<-1;
		return 0;
	}
	while(r-l>1e-6){
	    long double mid=(l+r)/2;
	if(check(mid))r=mid;
	else l=mid;
	}
	cout<<fixed<<setprecision(10)<<r;
	return 0;
}