#include <bits/stdc++.h>
#include <bits/extc++.h>
#define StarBurstStream ios_base::sync_with_stdio(false); cin.tie(0); cout.tie(0);
#define iter(a) a.begin(), a.end()
#define riter(a) a.rbegin(), a.rend()
#define lsort(a) sort(iter(a))
#define gsort(a) sort(riter(a))
#define pb(a) push_back(a)
#define eb(a) emplace_back(a)
#define pf(a) push_front(a)
#define ef(a) emplace_front(a)
#define pob pop_back()
#define pof pop_front()
#define mp(a, b) make_pair(a, b)
#define F first
#define S second
#define mt make_tuple
#define gt(t, i) get<i>(t)
#define tomax(a, b) ((a) = max((a), (b)))
#define tomin(a, b) ((a) = min((a), (b)))
#define topos(a) ((a) = (((a) % MOD + MOD) % MOD))
#define uni(a) a.resize(unique(iter(a)) - a.begin())
#define printv(a, b) {bool pvaspace=false; \
for(auto pva : a){ \
if(pvaspace) b << " "; pvaspace=true;\
b << pva;\
}\
b << "\n";}
using namespace std;
using namespace __gnu_pbds;
typedef long long ll;
typedef unsigned long long ull;
typedef long double ld;
using pii = pair<int, int>;
using pll = pair<ll, ll>;
using pdd = pair<ld, ld>;
using tiii = tuple<int, int, int>;
const ll MOD = 1000000007;
const ll MAX = 2147483647;
template<typename A, typename B>
ostream& operator<<(ostream& o, pair<A, B> p){
return o << '(' << p.F << ',' << p.S << ')';
}
ll ifloor(ll a, ll b){
if(b < 0) a *= -1, b *= -1;
if(a < 0) return (a - b + 1) / b;
else return a / b;
}
ll iceil(ll a, ll b){
if(b < 0) a *= -1, b *= -1;
if(a > 0) return (a + b - 1) / b;
else return a / b;
}
int n, K;
vector<int> a, b;
ld calc(int cnt){
//cerr << "calc " << cnt << "\n";
vector<vector<ld>> dp(cnt + 1, vector<ld>(n + 1, 1e87));
dp[0][0] = 0;
for(int i = 1; i <= n; i++){
for(int j = K; j >= 1; j--){
dp[cnt][j] = min(dp[cnt][j], dp[cnt][j - 1] + (ld)a[i] / (cnt + 1));
}
for(int j = cnt; j >= 0; j--){
if(j != cnt) dp[j][i] = min(dp[j][i], dp[j][i - 1] + (ld)a[i] / (cnt + 1));
if(j && b[i] != -1) dp[j][i] = min(dp[j][i], dp[j - 1][i - 1] + (ld)b[i] / j);
}
//cerr << "dp " << i << "\n";
//for(int j = 0; j <= cnt; j++) printv(dp[j], cerr);
}
//cerr << "calc ok " << dp[cnt][K] << "\n";
return dp[cnt][K];
}
int main(){
StarBurstStream
cin >> n >> K;
a.resize(n + 1);
b.resize(n + 1);
vector<pii> tmp(n + 1);
for(int i = 1; i <= n; i++) cin >> tmp[i].F >> tmp[i].S;
sort(tmp.begin() + 1, tmp.end(), [&](pii a, pii b){
if(a.S == b.S) return false;
if(a.S == -1) return false;
if(b.S == -1) return true;
return a.S < b.S;
});
for(int i = 1; i <= n; i++) tie(a[i], b[i]) = tmp[i];
ld ans = 1e87;
for(int i = 0; i <= K; i++) ans = min(ans, calc(i));
cout << fixed << setprecision(20) << ans << "\n";
return 0;
}
