#include<iostream>
#include<cstdio>
#include<cstring>
#include<string>
#include<algorithm>
#include<cmath>
#include<cstdlib>
#define maxn 1000010
#define eps 1e-6
using namespace std;
typedef long long ll;
typedef unsigned long wf;
typedef unsigned int u32;
typedef unsigned long long u64;
ll a[maxn],b[maxn],s=0,n,p,sum;
inline bool check(double x){
	double sum=0;
	for(int i=1;i<=n;i++)
		if(a[i]*x>b[i]) 
			sum+=a[i]*x-b[i];
	return sum<=x*p;
}
int main(){
	bool k=true;
	cin>>n>>p;
	for(int i=1;i<=n;i++)
		cin>>a[i]>>b[i],s+=a[i];
	if(n==1||s<p) cout<<"-1",k=false;
	else if(k==true){
		double l=0,r=1e10,mid;
		while(r-l>eps){
			mid=(l+r)/2;
			if(check(mid)) 
				l=mid;
			else 
				r=mid;
		}
		printf("%.10lf",l);
    }
	return 0;
}

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