#include <bits/stdc++.h>
#pragma GCC optimize("O3")
#define int long long
#define ll long long
#define se second
#define fi first
#define pb push_back
#define lf (id<<1)
#define rg ((id<<1)|1)
#define md ((l+r)>>1)
#define ld long double
using namespace std;
typedef pair<int,int> pii;
typedef pair<pii,pii> ipii;
const int MAXN = 5e5+10;
const int MAXA = 5e5+10;
const int SQRT = 450;
const ld INF = 1e16;
const int MOD = 1e9+7;
const int LOG = 60;
int sum(int a, int b){ return (a+MOD+b)%MOD; }
void chsum(int &a, int b){ a = sum(a,b); }
int mul(int a, int b){ return (a*b)%MOD; }
void chmul(int &a, int b){ a = mul(a,b); }
void chmn(auto &a, auto b){ a = min(a, b); }
void chmx(auto &a, auto b){ a = max(a, b); }
vector<int> dx = {0, 0, -1, 1};
vector<int> dy = {1, -1, 0, 0};
int n, need, a[MAXN], b[MAXN], pr[MAXN], blm[MAXN], cost[MAXN];
ld dp[510][510], ba[510][510];
ld ANS = INF;
void solve(int sp){
// sort based on b
// dp dari depan, kurangin a[i]/sp tambahin b
// dari belakang, tambahin b
for(int i=0; i<=n+1; i++)
for(int j=0; j<=n+1; j++)
dp[i][j] = INF;
dp[0][0] = 0;
for(int i=1; i<=n; i++){
for(int j=0; j<=sp; j++){ // b yg udh diambil segini
dp[i][j] = dp[i-1][j];
if(j!=0 && cost[i]!=INF){ // ambil
chmn(dp[i][j], dp[i-1][j-1]
- (ld)blm[i]/(sp+1) + (ld)cost[i]/j);
}
}
}
for(int i=0; i<=n+1; i++)
for(int j=0; j<=n+1; j++) ba[i][j] = INF;
ba[n+1][sp+1] = 0;
for(int i=n; i>=1; i--){
for(int j=sp+1; j>=1; j--){ // b nya yg segini
ba[i][j] = ba[i+1][j];
if(j!=sp+1 && cost[i]!=INF){
chmn(ba[i][j], ba[i+1][j+1]
+ (ld)cost[i]/j);
}
}
}
for(int i=0; i<=need; i++){
for(int j=0; j<=sp; j++){
ld mn = dp[i][j] + ba[i+1][j+1] + (ld)pr[need]/(sp+1);
chmn(ANS, mn);
}
}
}
signed main(){
ios_base::sync_with_stdio(0);cin.tie(0);cout.tie(0);
cin>>n>>need;
vector<pii> vec; vec.pb({-1,-1});
vector<pii> cc; cc.pb({-1, -1});
for(int i=1; i<=n; i++){
cin>>a[i]>>b[i];
if(b[i] == -1) b[i] = INF;
vec.pb({a[i], b[i]});
cc.pb({b[i], a[i]});
}
sort(vec.begin(), vec.end());
for(int i=1; i<=n; i++){
a[i] = vec[i].fi, b[i] = vec[i].se;
pr[i] = pr[i-1]+a[i];
}
sort(cc.begin(), cc.end());
for(int i=1; i<=n; i++)
cost[i] = cc[i].fi, blm[i] = cc[i].se;
for(int sp=0; sp<=need; sp++)
solve(sp);
cout << fixed << setprecision(5) << ANS << '\n';
}
