#include<bits/stdc++.h>
#include<fstream>
#pragma GCC optimize("Ofast,O3,unroll-loops")
#pragma GCC target("avx2")
using namespace std;
//ifstream fin("FEEDING.INP");
//ofstream fout("FEEDING.OUT");
#define sz(a) (int)a.size()
#define ll long long
#define pb push_back
#define forr(i, a, b) for(int i = a; i < b; i++)
#define dorr(i, a, b) for(int i = a; i >= b; i--)
#define ld long double
#define vt vector
#include<fstream>
#define fi first
#define se second
#define pll pair<ll, ll>
#define pii pair<int, int>
const int base = 74;
const ll mod = 1e9 + 7, inf = 1e18, mxv = 1005, mxn = 2e5 + 5;
int n, k;
mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());
ld dp[505][505];
pll p[mxn + 1];
bool cmp(pll &a, pll &b){
return(a.se < b.se);
}
ld get(int x){
for(int i = 1; i <= n; i++){
for(int j = 0; j <= min(i, x); j++){
dp[i][j] = inf;
int other = i - j;
if(other <= k - x){
dp[i][j] = dp[i - 1][j] + (ld)p[i].se / (other);
}else{
dp[i][j] = dp[i - 1][j];
}
other = min(other, k - x);
if(j > 0){
dp[i][j] = min(dp[i][j], dp[i - 1][j - 1] + (ld)p[i].fi / (k - x + 1));
}
}
}
return(dp[n][x]);
}
signed main()
{
ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);
cin >> n >> k;
for(int i = 1; i <= n; i++){
cin >> p[i].fi >> p[i].se;
if(p[i].se == -1)p[i].se = 1e15;
}
sort(p + 1, p + n + 1, cmp);
int l = 0, r = k;
ld ans = inf;
while(l <= r){
int m1 = l + (r - l) / 3, m2 = r - (r - l) / 3;
ld val1 = get(m1), val2 = get(m2);
if(val1 < val2){
ans = val1; r = m2 - 1;
}else if(val1 > val2){
ans = val2; l = m1 + 1;
}else{
r = m2 - 1; l = m1 + 1;
}
}
cout << fixed << setprecision(10) << ans;
return(0);
}
