import java.io.*;
import java.util.*;

public class donthungertogether_suhas {
    static class food{
        double quantity; int expiration;
        public food(double q, int e){
            this.quantity = q;
            this.expiration = e;
        }
    }
    public static void main(String[] args){
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int k = sc.nextInt();
        food[] arr = new food[n];
        double r = 0;
        for (int i = 0; i < n; i++){
            arr[i] = new food(sc.nextInt(), sc.nextInt());
            r = Math.max(r,arr[i].quantity);
        }
        double l = 0;
        for (int i = 0; i < 60; i++){ // adjust?
            double mid = (l+r)/2.0;
            PriorityQueue<food> pq = new PriorityQueue<>((o1,o2) -> o1.expiration-o2.expiration);
            boolean works = true;
            for (int j = 0; j < n; j++){
                pq.add(arr[j]);
                double needToEat = mid;
                while (!pq.isEmpty() && needToEat != 0){
                    food next = pq.remove();
                    if (j+1 > next.expiration){
                        continue;
                    }
                    double eatVal = Math.min(needToEat,next.quantity);
                    needToEat -= eatVal;
                    food addBack = new food(next.quantity-eatVal,next.expiration);
                    if (addBack.quantity > 0) pq.add(addBack);
                }
                if (needToEat != 0) {
                    works = false;
                    break;
                }
            }
            if (works){
                l = mid;
            }else{
                r = mid;
            }
        }
        if (l == 0){
            System.out.println(-1);
        }else {
            System.out.println(l / k);
        }
    }

}