#include <bits/stdc++.h>
#pragma GCC optimize ("Ofast", "unroll-loops")
using namespace std;
#define ll long long
#define int ll
#define FOR(i,a,b) for (int i = (a); i<(b); i++)
#define REP(i,n) FOR(i,0,n)
#define REP1(i,n) FOR(i,1,n+1)
#define RREP(i,n) for (int i=(n)-1; i>=0; i--)
#define f first
#define s second
#define pb push_back
#define ALL(x) x.begin(),x.end()
#define SZ(x) (int)(x.size())
#define SQ(x) (x)*(x)
#define pdd pair<double ,double>
#define pii pair<int, int>
#define pcc pair<char, char>
#define endl '\n'
//#define TOAD
#ifdef TOAD
#define bug(x) cerr<<__LINE__<<": "<<#x<<" is "<<x<<endl
#define IOS()
#else
#define bug(...)
#define IOS() ios::sync_with_stdio(0), cin.tie(0), cout.tie(0)
#endif
const ll inf = 1ll<<60;
const int iinf=2147483647;
const ll mod = 1e9+7;
const ll maxn=105;
const double PI=acos(-1);
ll pw(ll x, ll p, ll m=mod){
ll ret=1;
while (p>0){
if (p&1){
ret*=x;
ret%=m;
}
x*=x;
x%=m;
p>>=1;
}
return ret;
}
ll inv(ll a, ll m=mod){
return pw(a,m-2);
}
//=======================================================================================
double dp[maxn][maxn][maxn];
bool cmp(pdd x, pdd y){
if (x.s==y.s&&x.s==-1){
return x.f<y.f;
}
if (x.s==-1||y.s==-1){
return x.s>y.s;
}
return x.s<y.s;
}
signed main (){
IOS();
cout<<fixed<<setprecision(9);
int n, K; cin>>n>>K;
vector<pdd> vc(n+1), ov(n);
REP1(i,n){
cin>>vc[i].f>>vc[i].s;
ov[i-1]=vc[i];
}
sort(ALL(vc), cmp);
bool ok=1;
REP1(i,n){
if (vc[i].s==-1||vc[i].f==vc[i].s){
}
else ok=0;
}
if (ok){
int k=K;
int pos=0;
double res=inf;
sort(ALL(ov), cmp);
if (ov[0].s==ov[n-1].s&&ov[0].s==-1){
int res=0;
REP(i,k){
res+=ov[i].f;
}
cout<<res<<endl;
return 0;
}
REP(i,n){
if (ov[i].s==-1){
break;
}
pos++;
}
REP(i,min(k+1, pos+1)){
//cout<<i<<endl;
double cur=0;
REP(j,i){
//cout<<j<<endl;
//cout<<vc[i].f/(j+1)<<endl;
cur+=ov[j].f/(0.0+j+1);
//cout<<cur<<endl;
}
//cout<<cur<<endl;
if (cur==inf||pos+(k-i)-1>=n) continue;
REP(j, k-i){
//cout<<j+pos<<endl;
cur+=ov[pos+j].f/(0.0+i+1);
//cout<<cur<<endl;
}
res=min(res, cur);
}
cout<<res<<endl;
return 0;
}
double ans=inf;
REP(k, K+1){
/*if (k==0){
vector<double> cur;
REP1(i,n) cur.pb(vc[i].f);
sort(ALL(cur));
REP1(i, K){
ans+=cur[i];
}
continue;
}
*/
/*dp[1][1][1]=vc[1].s;
dp[1][1][0]=vc[1].f/k;
dp[1][0][0]=0;
*/
REP(i,maxn){
REP(j,maxn){
REP(l,maxn){
dp[i][j][l]=inf;
}
}
}
dp[1][1][1]=vc[1].s;
dp[1][1][0]=vc[1].f/(k+1);
dp[1][0][0]=0;
FOR(i,2,n+1){
dp[i][0][0]=0.0;
FOR(j, 1, i+1){
dp[i][j][0]=min(dp[i-1][j-1][0]+vc[i].f/(k+1), dp[i-1][j][0]);
FOR(l, 1, j+1){
if (vc[i].s==-1){
dp[i][j][l]=min(dp[i-1][j-1][l]+vc[i].f/(k+1), dp[i-1][j][l]);
}
else dp[i][j][l]=min({dp[i-1][j-1][l-1]+vc[i].s/l, dp[i-1][j-1][l]+vc[i].f/(k+1), dp[i-1][j][l]});
}
}
}
ans=min(ans, dp[n][K][k]);
}
cout<<ans<<endl;
}
