#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using ld = long double;
#define fi first
#define se second
#define vi vector<int>
#define vll vector<long long>
#define pii pair<int, int>
#define pll pair<long long, long long>
#define pb push_back
#define mp make_pair
#define eb emplace_back
#define all(x) (x).begin(), (x).end()
#define sz(x) (int)(x).size()
mt19937 rng(chrono::high_resolution_clock::now().time_since_epoch().count());
mt19937_64 rng64(chrono::high_resolution_clock::now().time_since_epoch().count());
inline int rand(int l,int r){return uniform_int_distribution<int>(l, r)(rng);}
inline ll rand(ll l,ll r){return uniform_int_distribution<ll>(l, r)(rng64);}
#ifdef DEBUG
auto&operator<<(auto&o,pair<auto,auto>p){return o<<"("<<p.first<<", "<<p.second<<")";}
auto operator<<(auto&o,auto x)->decltype(x.end(),o){o<<"{";int i=0;for(auto e:x)o<<","+!i++<<e;return o<<"}";}
#define debug(X...)cerr<<"["#X"]: ",[](auto...$){((cerr<<$<<"; "),...)<<endl;}(X)
#else
#define debug(...){}
#endif
struct custom_hash {
static uint64_t splitmix64(uint64_t x) {
x += 0x9e3779b97f4a7c15;
x = (x ^ (x >> 30)) * 0xbf58476d1ce4e5b9;
x = (x ^ (x >> 27)) * 0x94d049bb133111eb;
return x ^ (x >> 31);
}
size_t operator()(uint64_t x) const {
static const uint64_t FIXED_RANDOM = chrono::steady_clock::now().time_since_epoch().count();
return splitmix64(x + FIXED_RANDOM);
}
};
const int INF = 1e9;
int n, m;
vector<pii> a;
bool comp(pii& x, pii& y){
if(x.se != y.se){
return x.se < y.se;
}
return x.fi < y.fi;
}
int main(){
ios_base::sync_with_stdio(0);
cin.tie(NULL);
cout.tie(NULL);
cin >> n >> m;
a.resize(n);
for(int i = 0; i < n; i++){
cin >> a[i].fi >> a[i].se;
if(a[i].se == -1){
a[i].se = INF;
}
}
sort(all(a), comp);
ld ans = (ld)INF;
for(int k = 0; k <= m; k++){
vector<ld> dp(m - k + 1, (ld)INF);
dp[0] = 0;
ld p, val;
for(int i = 0; i < n; i++){
for(int j = min(m - k, i + 1); j >= 0; j--){
p = dp[j];
if(j > 0){
val = (ld)dp[j - 1] + (ld)a[i].fi / (k + 1);
}else{
val = (ld)INF;
}
if(i - j + 1 <= 0){
dp[j] = min(val, p);
}else if(i - j + 1 > k){
dp[j] = min(val, p);
}else{
dp[j] = min(val, (ld)p + (ld)a[i].se / (i - j + 1));
}
}
}
ans = min(ans, dp[m - k]);
}
cout << fixed << setprecision(9);
cout << ans<< '\n';
return 0;
}
