#include <bits/stdc++.h>
using namespace std;
#define int long long
#define ld long double
vector <pair <ld, ld>> arr = {};
vector <vector <ld>> dp(502, vector <ld>(502, -1));
ld dps(int cur, int n, int k, int ck, int cuk, int cak) {
if(cur == n) {
if(ck == cuk) {
return 0;
}
return 1e18;
}
if(dp[cur][cuk] != -1) {
return dp[cur][cuk];
}
ld totalm = 1e18;
if(cuk < ck) {
ld a = cuk+1;
ld data = dps(cur+1, n, k, ck, cuk+1, cak)+(arr[cur].second/(a));
// if(ck == 1 && cur == 0) {
// // cout << a << " " << data << " " << totalm << " " << arr[cur].second << endl;
// }
totalm = min(totalm, data);
}
// if((cuk+cak) < k) {
ld a = ck+1;
ld data = dps(cur+1, n, k, ck, cuk, cak+1)+(arr[cur].first/a);
// if(ck == 1 && cuk == 1 && cur == 1) {
// cout << a << " " << data << " " << cak << " " << arr[cur].second << " " << totalm << endl;
// }
totalm = min(totalm, data);
// }
// ld data = dps(cur+1, n, k, ck, cuk, cak);
// totalm = min(totalm, data);
return dp[cur][cuk] = totalm;
}
signed main() {
//your code goes here
int n;
cin >> n;
int k;
cin >> k;
for(int i = 0; i < n; i++) {
ld a, b;
cin >> a >> b;
if(b == -1) {
b = 1e18;
}
arr.push_back({a, b});
}
sort(arr.begin(), arr.end(), [&](auto& left, auto& right) {
return left.second < right.second;
});
// for(int i = 0; i < n; i++) {
// cout << arr[i].first << " " << arr[i].second << endl;
// }
ld totalm = 1e18;
for(int i = 0; i <= k; i++) {
for(int i = 0; i <= n; i++) {
for(int j = 0; j <= k; j++) {
// for(int l = 0; l <= k; l++) {
dp[i][j] = -1;
// }
}
}
ld data = dps(0, n, k, i, 0, 0);
totalm = min(totalm, data);
// cout << data << endl;
}
cout << totalm << endl;
return 0;
}
