#include "bits/stdc++.h"
using namespace std;
//#define int long long
const int MAXN = 3e5 + 10;
const int MOD = 998244353;
mt19937_64 rng((int)std::chrono::steady_clock::now().time_since_epoch().count());
int rnd(int x, int y) {
int u = uniform_int_distribution<int>(x, y)(rng); return u;
}
bool cmp(pair<int, int> x, pair<int, int> y) {
return x.second < y.second;
}
int n, k, a[MAXN], b[MAXN];
double fun(int bcnt) {
double dp[k - bcnt + 1][bcnt + 1][n + 1]; // type A, type B, prefix
for(int i=0; i<=k-bcnt; i++) {
for(int j=0; j<=bcnt; j++) {
for(int l=0; l<=n; l++) {
dp[i][j][l] = 1e9;
}
}
}
for(int i=0; i<=n; i++) dp[0][0][i] = 0;
for(int i=0; i<=k-bcnt; i++) {
for(int j=0; j<=bcnt; j++) {
if(i == 0 && j == 0) continue;
for(int l=i+j; l<=n; l++) {
// register as type A
if(i > 0) dp[i][j][l] = dp[i-1][j][l-1] + a[l] * 1.0 / (bcnt + 1);
// register as type B
if(j > 0 && b[l] != 1226) dp[i][j][l] = min(dp[i][j][l], dp[i][j-1][l-1] + b[l] * 1.0 / j);
// register as neither
dp[i][j][l] = min(dp[i][j][l], dp[i][j][l-1]);
}
}
}
return dp[k-bcnt][bcnt][n];
}
void solve(int tc) {
cin >> n >> k;
pair<int, int> p[n+1];
for(int i=1; i<=n; i++) {
cin >> p[i].first >> p[i].second;
if(p[i].second == -1) p[i].second = 1226;
}
sort(p+1, p+n+1, cmp);
for(int i=1; i<=n; i++) {
a[i] = p[i].first, b[i] = p[i].second;
}
int lb = 0, rb = k;
double res[k+1];
for(int i=0; i<=k; i++) res[i] = -1;
while(lb < rb) {
int mid = (lb + rb) >> 1;
double f0 = (res[mid] < 0 ? fun(mid) : res[mid]);
double f1 = (res[mid+1] < 0 ? fun(mid+1) : res[mid+1]);
if(f0 > f1) lb = mid+1;
else rb = mid;
}
cout << fixed << setprecision(10) << (res[lb] < 0 ? fun(lb) : res[lb]) << "\n";
}
int32_t main() {
ios::sync_with_stdio(0); cin.tie(0);
int t = 1; //cin >> t;
for(int i=1; i<=t; i++) solve(i);
}
