其实还是01分数规划，因为要输出分数形式，所以要用结构体存数据，一起排序，每次记录分子分母，最后在输出就好啦

#include<cstdio>
#include<algorithm>
#include<iostream>
using namespace std;
const int maxn = 1e5+5;
int k,n;
const double eps = 1e-6;
int ta,tb;
struct node{
    int a,b;
    double c;
    bool operator < (const node &t)const{
        return c>t.c;
    }
}p[maxn];
bool check(double mid)
{
	double ans = 0; ta=tb = 0;
	for(int i = 0; i<n; i++)
		p[i].c = p[i].a - mid*p[i].b;
	sort(p,p+n);
	for(int i = 0; i<k; i++)
		ans  += p[i].c,ta+=p[i].a,tb+=p[i].b;
	return ans>=0;
}
void solve ()
{
	double l = 0,r = 1000000000;
	while(r-l>eps)
	{
		double mid = (l+r)/2;
		if(check(mid)) l = mid;
		else r = mid;
	}
	//printf("%lf\n",l);
}
int main()
{
    //freopen("in.txt","r",stdin);
	scanf("%d%d",&n,&k); 
	for(int i = 0; i<n; i++)
	{
		scanf("%d%d",&p[i].b,&p[i].a);
	}
	solve();
    int t = __gcd(ta,tb);
    printf("%d/%d",ta/t,tb/t);
	return 0;
}