#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef pair<int,int> ii;
typedef pair<ll,ll> pll;
typedef vector<int> vi;
typedef vector<ii> vii;
typedef vector<ll> vll;
typedef vector<pll> vpll;
#define PB push_back
#define PF push_front
#define PPB pop_back
#define PPF pop_front
#define X first
#define Y second
#define MP make_pair
#define all(x) (x).begin(), (x).end()
const int mod = 1e9 + 7; //998244353;
const int inf = 1e9 + 7;
const ll INF = 1e18 + 7;
const int logo = 20;
const int MAXN = 700;
const int off = 1 << logo;
const int trsz = off << 1;
const int dx[] = {1, -1, 0, 0};
const int dy[] = {0, 0, -1, 1};
typedef long double ld;
typedef pair<ld, ld> pld;
const ld eps = 1e-15;
vector<pld> arr;
ld dp[MAXN][MAXN];
bool cmp(pld &a, pld &b){
if(abs(a.Y - b.Y) > eps) return a.Y < b.Y;
return a.X < b.X;
}
void solve(){
int n, k;
cin >> n >> k;
arr.resize(n);
for(auto &x : arr){
cin >> x.X >> x.Y;
if(x.Y == -1) x.Y = (ld)inf;
}
sort(all(arr), cmp);
//L - broj pomocnika
//R - broj obicnih
ld ans = inf;
for(int L=0; L<=k; L++){
for(int i=0; i<=n; i++) for(int j=0; j<=n; j++) dp[i][j] = (ld)inf;
dp[0][0] = 0;
for(int i=1; i<=n; i++){
pld cur = arr[i - 1];
for(int R=0; R<=min(i, k - L); R++){
int clef = i - R;
if(R) dp[i][R] = min(dp[i][R], dp[i - 1][R - 1] + (ld)cur.X / (ld)(L + 1));
if(clef <= L) dp[i][R] = min(dp[i][R], dp[i - 1][R] + (ld)cur.Y / (ld)clef);
else dp[i][R] = min(dp[i][R], dp[i - 1][R]);
}
}
ans = min(ans, dp[n][k - L]);
}
cout << fixed << setprecision(10) << ans << "\n";
}
int main(){
ios_base::sync_with_stdio(false);
cin.tie(NULL);
cout.tie(NULL);
int tt = 1;
//cin >> tt;
while(tt--) solve();
return 0;
}
