#19???????

#include<bits/stdc++.h>
using namespace std;
double n,p,a[1000005],b[1000005];
double inf=0.0000000001;
inline bool ck(double x){
    double sum=0;
    for(int i=1;i<=n;i++){
        if(x*a[i]<=b[i])continue;
        sum+=(x*a[i]-b[i]);
    }
    return sum<=p*x;
}
int main(){
    cin>>n>>p;
    double sum=0;
    for(int i=1;i<=n;i++)cin>>a[i]>>b[i],sum+=a[i];
    if(sum<=p){
        cout<<-1;
        return 0;
    }
    double l=0,r=1<<30,mid;
    while(r-l>=inf){
        mid=(l+r)/2;
        if(ck(mid)){
            l=mid;
        }else{
            r=mid;
        }
    }
    printf("%.10lf",l);
}