// Hallelujah, praise the one who set me free
// Hallelujah, death has lost its grip on me
// You have broken every chain, There's salvation in your name
// Jesus Christ, my living hope
#include <bits/stdc++.h>
using namespace std;
#pragma GCC optimize("O3,unroll-loops")
#pragma GCC target("avx2,bmi,bmi2,popcnt,lzcnt")
#define REP(i, s, e) for (int i = (s); i < (e); i++)
#define RREP(i, s, e) for (int i = (s); i >= (e); i--)
template <class T>
inline bool mnto(T& a, T b) {return a > b ? a = b, 1 : 0;}
template <class T>
inline bool mxto(T& a, T b) {return a < b ? a = b, 1: 0;}
typedef long long ll;
typedef double ld;
#define FI first
#define SE second
typedef pair<int, int> ii;
typedef pair<ll, ll> pll;
typedef tuple<int, int, int> iii;
#define ALL(_a) _a.begin(), _a.end()
#define SZ(_a) (int) _a.size()
#define pb push_back
typedef vector<int> vi;
typedef vector<ll> vll;
typedef vector<ii> vii;
typedef vector<iii> viii;
#ifndef DEBUG
#define cerr if (0) cerr
#endif
const int INF = 1000000005;
const ll LINF = 1000000000000000005ll;
const int MAXN = 505;
int n, k, m;
int a[MAXN], b[MAXN];
int aid[MAXN], bid[MAXN];
bool done[MAXN];
ld dp[MAXN][MAXN], pa[MAXN][MAXN], pb[MAXN][MAXN];
ld ans;
ld calc(int i) {
REP (l, 0, n + 1) {
REP (o, 0, n + 1) {
dp[l][o] = INF;
}
}
dp[0][0] = 0;
REP (j, 1, n + 1) {
RREP (l, min(i, j), 0) {
RREP (o, min(k - i, j - l), 0) {
if (o) {
mnto(dp[l][o],
dp[l][o - 1] + pa[i][j]);
//dp[l][o - 1] + a[bid[j]] / (ld) (i + 1));
}
if (l && b[bid[j]] != -1) {
mnto(dp[l][o],
dp[l - 1][o] + pb[j][l]);
//dp[l - 1][o] + b[bid[j]] / (ld) l);
}
//cerr << j << ' ' << l << ' ' << o << ": " << dp[j][l][o] << '\n';
}
}
}
//cerr << i << ": " << dp[n][i][k - i] << '\n';
return dp[i][k - i];
}
int main() {
#ifndef DEBUG
ios::sync_with_stdio(0), cin.tie(0);
#endif
cin >> n >> k;
REP (i, 1, n + 1) {
cin >> a[i] >> b[i];
if (b[i] != -1) {
m++;
}
}
iota(aid + 1, aid + n + 1, 1);
iota(bid + 1, bid + n + 1, 1);
sort(aid + 1, aid + n + 1, [&] (int l, int r) {
return a[l] < a[r];
});
sort(bid + 1, bid + n + 1, [&] (int l, int r) {
return b[l] < b[r];
});
ans = INF;
REP (i, 0, min(k, m) + 1) {
REP (j, 1, n + 1) {
pa[i][j] = a[bid[j]] / (ld) (i + 1);
pb[j][i] = b[bid[j]] / (ld) i;
}
}
int lo = 0, hi = min(k, m);
while (hi - lo > 2) {
int mid1 = lo + (hi - lo) / 3, mid2 = lo + (hi - lo) / 3 * 2;
if (calc(mid1) < calc(mid2)) {
hi = mid2;
} else {
lo = mid1;
}
}
REP (i, lo, hi + 1) {
mnto(ans, calc(i));
}
cout << setprecision(10) << ans << '\n';
return 0;
}
