#include<iostream>
using namespace std;
int n;
double a[100005] , b[100005] , p , sum;
double l , r = 1e10, mid;
bool p1(int ans){
	double q = p * ans;
	double sum;
	for(int i=0;i<n;i++){
		if(a[i]*ans<=b[i]){
			continue;
		}
		sum += (a[i]*ans-b[i]);
	}
	return sum <= q;
}
int main(){
	cin >> n >> p;
	for(int i=0;i<n;i++){
		cin >> a[i] >> b[i];
		sum += a[i];
	}
	if(sum<=p){
		cout << -1.0000000000;
		return 0;
	}
	while(r-l>1e-6){
		mid = (l + r) / 2;
		if(p1(mid)){
			l = mid;
		}else{
			r = mid;
		}
	}
	cout << l;
	return 0;
}