#include <iostream>
#include <cstdio>
#include <cstring>
#include <algorithm>
#include <cmath>
#include <queue>
#include <stack>
#include <map>
#include <set>
#include <vector>
#define rep(i,x,n) for(int i=x;i<n;i++)
#define repd(i,x,n) for(int i=x;i<=n;i++)
#define pii pair<int,int>
#define pll pair<long long ,long long>
#define gbtb std::ios::sync_with_stdio(false)
#define MS0(X) memset((X), 0, sizeof((X)))
#define MSC0(X) memset((X), '\0', sizeof((X)))
#define pb push_back
#define mp make_pair
#define fi first
#define se second
#define gg(x) getInt(&x)
#define eps 1e-6
using namespace std;
typedef long long ll;
inline void getInt(int* p);
const int maxn=1000010;
const int inf=0x3f3f3f3f;
/*** TEMPLATE CODE * * STARTS HERE ***/
struct node
{int h;int x;
}a[maxn];
int n,p;
bool check(double mid)
{double need=0.0000;double sum=0.00000;repd(i,1,n){need=mid*a[i].x-a[i].h;if(need>0.0000000){sum+=need;}else{}}return 1.000000*mid*p-sum>0.000000;
}
int main()
{gg(n),gg(p);ll sum=0ll;repd(i,1,n){gg(a[i].x);gg(a[i].h);sum+=(1ll*a[i].x);}if(sum<=p){printf("-1\n");}else{double l=0.0000;double r=1e10;double mid;double ans;while(r-l>eps){mid=(r+l)/2.00000;if(check(mid)){l=mid;ans=l;}else{r=mid-eps;}}printf("%.5lf\n", ans);}return 0;
}inline void getInt(int* p) {char ch;do {ch = getchar();} while (ch == ' ' || ch == '\n');if (ch == '-') {*p = -(getchar() - '0');while ((ch = getchar()) >= '0' && ch <= '9') {*p = *p * 10 - ch + '0';}}else {*p = ch - '0';while ((ch = getchar()) >= '0' && ch <= '9') {*p = *p * 10 + ch - '0';}}
}