#include <bits/stdc++.h>
using namespace std;
#define INFTY 1000000069
bool comp(pair<int,int> a, pair<int,int> b) {
if(a.first == -1) return false;
if(b.first == -1) return true;
return a < b;
}
int main() {
ios_base::sync_with_stdio(false); cin.tie(0);
int N, K; cin >> N >> K; int A[N], B[N]; pair<int, int> data[N];
for(int i = 0; i < N; i++) {cin >> data[i].second >> data[i].first;}
sort(data, data + N, comp);
for(int i = 0; i < N; i++) {
A[i] = data[i].second;
B[i] = data[i].first;
}
float mn = INFTY;
float dp[N + 1][K + 1][2];
for(int i = 0; i <= N; i++) for(int j = 0; j <= K; j++) for(int k = 0; k < 2; k++) dp[i][j][k] = INFTY;
for(int g = 0; g <= K; g++) {
dp[0][0][0] = 0; if(g == 0) dp[0][0][1] = 0;
for(int i = 1; i <= N; i++) for(int j = 0; j <= K; j++) {
if(i - j >= 0 && i - j <= g) {
if(i - j == g) dp[i][j][0] = min(dp[i][j][0], dp[i - 1][j][1]);
if(j > 0) {
dp[i][j][0] = min(dp[i][j][0], dp[i - 1][j - 1][0] + A[i - 1] / (float)(g + 1));
}
if(i - j > 0 && B[i - 1] != -1) {
dp[i][j][0] = min(dp[i][j][0], dp[i - 1][j][0] + B[i - 1] / (float)(i - j));
}
}
if(g + j <= i) {
dp[i][j][1] = min(dp[i][j][1], dp[i - 1][j][1]);
if(j > 0) {
dp[i][j][1] = min(dp[i][j][1], dp[i - 1][j - 1][1] + A[i - 1] / (float)(g + 1));
}
if(B[i - 1] != -1 && g + j == i) {
dp[i][j][1] = min(dp[i][j][1], dp[i - 1][j][0] + B[i - 1] / (float)g);
}
}
}
mn = min(mn, dp[N][K - g][1]);
for(int i = 0; i <= N; i++) for(int j = 0; j <= K; j++) {
dp[i][j][0] = INFTY;
dp[i][j][1] = INFTY;
}
}
cout << mn;
}
