#include<iostream>

#include<cstdlib>

#include<cstring>

#include<cstdio>

#include<algorithm>

#include<queue>

#include<cmath>

#include<map>

#define ll long long

using namespace std;

const int maxn=,inf=1e9;

struct poi{double sum;int pos;}d[maxn];

int n,K,ansx,ansy,x,y;

int p[maxn],w[maxn];

double mid;

void read(int &k)

{

    int f=;k=;char c=getchar();

    while(c<''||c>'')c=='-'&&(f=-),c=getchar();

    while(c<=''&&c>='')k=k*+c-'',c=getchar();

    k*=f;

}

bool cmp(poi a,poi b){return a.sum-b.sum>1e-;}

bool check()

{

    for(int i=;i<=n;i++)d[i].sum=1.0*p[i]-1.0*mid*w[i],d[i].pos=i;

    sort(d+,d++n,cmp);

    double sum=0.0;x=y=;

    for(int i=;i<=K;i++)

    {

        x+=p[d[i].pos];y+=w[d[i].pos];

        sum+=d[i].sum;

    }

    if(sum>=)return ;

    return ;

}

ll gcd(ll a,ll b){return b?gcd(b,a%b):a;}

int main()

{

    read(n);read(K);

    for(int i=;i<=n;i++)read(w[i]),read(p[i]);

    double l=,r=;

    while(r-l>1e-)

    {

        mid=(l+r)/;

        if(check())l=mid,ansx=x,ansy=y;

        else r=mid;

    }

    ll d=gcd(ansx,ansy);

    printf("%lld/%lld",ansx/d,ansy/d);

    return ;

}