#include <iostream>
#include <vector>
#include <algorithm>
#include <limits>
#include <cmath>
using namespace std;
int n, k;
vector<int> start, endt;
vector<vector<int>> sm;
double dp(int i, int col, int mxCol, vector<vector<double>>& memo) {
if (col == mxCol) {
if (k - i < 0 || k - i > n) return numeric_limits<double>::infinity();
return static_cast<double>(sm[i][k - i]) / (mxCol + 1);
}
if (i == n) return numeric_limits<double>::infinity();
if (memo[i][col] != -1) return memo[i][col];
double x = dp(i + 1, col + 1, mxCol, memo) + (static_cast<double>(endt[i]) / (col + 1));
double y = dp(i + 1, col, mxCol, memo) + (static_cast<double>(start[i]) / (mxCol + 1));
memo[i][col] = min(x, y);
return memo[i][col];
}
double f(int col) {
vector<vector<double>> memo(n + 1);
for (int i = 0; i <= n; i++) { memo[i] = vector<double>(i+1, -1); }
return dp(0, 0, col, memo);
}
int main() {
cin >> n >> k;
start.resize(n);
endt.resize(n);
vector<pair<int, int>> pairs(n);
for (int i = 0; i < n; ++i) {
int a, b;
cin >> a >> b;
if (b == -1) b = numeric_limits<int>::max();
pairs[i] = {a, b};
}
sort(pairs.begin(), pairs.end(), [](const pair<int, int>& p1, const pair<int, int>& p2) {
if (p1.second != p2.second) return p1.second < p2.second;
return p1.first > p2.first;
});
for (int i = 0; i < n; ++i) {
start[i] = pairs[i].first;
endt[i] = pairs[i].second;
}
sm.assign(n + 1, vector<int>(n + 1, 0));
for (int i = n - 1; i >= 0; --i) {
for (int c = 1; c <= n; ++c) {
if ((n - i) < c) {
sm[i][c] = numeric_limits<int>::max();
continue;
}
if (i == n - 1) {
sm[i][c] = start[i];
} else {
if (sm[i + 1][c - 1] == numeric_limits<int>::max())
sm[i][c] = sm[i + 1][c];
else
sm[i][c] = min(sm[i + 1][c - 1] + start[i], sm[i + 1][c]);
}
}
}
double res = numeric_limits<double>::infinity();
int l = 0, r = n;
for (int mxCol = 0; mxCol <= n; ++mxCol) {
res = min(res, f(mxCol));
}
cout << fixed << res << endl;
return 0;
}
