//Sylwia Sapkowska
#include <bits/stdc++.h>
#pragma GCC optimize("O3", "unroll-loops")
using namespace std;
void __print(int x) {cerr << x;}
void __print(long long x) {cerr << x;}
void __print(long double x) {cerr << x;}
void __print(char x) {cerr << '\'' << x << '\'';}
void __print(const char *x) {cerr << '\"' << x << '\"';}
void __print(const string &x) {cerr << '\"' << x << '\"';}
void __print(bool x) {cerr << (x ? "true" : "false");}
template<typename T, typename V>
void __print(const pair<T, V> &x) {cerr << '{'; __print(x.first); cerr << ", "; __print(x.second); cerr << '}';}
template<typename T>
void __print(const T &x) {int f = 0; cerr << '{'; for (auto &i: x) cerr << (f++ ? ", " : ""), __print(i); cerr << "}";}
void _print() {cerr << "]\n";}
template <typename T, typename... V>
void _print(T t, V... v) {__print(t); if (sizeof...(v)) cerr << ", "; _print(v...);}
#ifdef LOCAL
#define debug(x...) cerr << "[" << #x << "] = ["; _print(x)
#else
#define debug(x...)
#endif
#define int long long
typedef pair<int, int> T;
typedef long double ld;
const int oo = 1e18, oo2 = 1e9+7, K = 30;
const int mod = 998244353;
void solve(){
int n, k; cin >> n >> k;
vector<T>tab;
tab.emplace_back(-oo, -oo);
for (int i = 1; i<=n; i++){
int x, y; cin >> x >> y;
if (y == -1) y = oo2;
tab.emplace_back(x, y);
}
sort(tab.begin(), tab.end(),[](auto x, auto y){return x.second == y.second ? x.first < y.first : x.second < y.second;});
vector dp(k+1, vector<ld>(n+1, oo));
dp[0][1] = 0;
for (int i = 1; i<=n; i++){
auto [a, b] = tab[i];
vector new_dp(k+1, vector<ld>(n+1, oo));
for (int ck = 0; ck <= k; ck++){
for (int col = 1; col <= n; col++){
//dp[i][ck][col]-->
//nic nie robimy --> dokladamy glos --> dokladamy glos i kolaboranta
new_dp[ck][col] = min({dp[ck][col],
(ck ? dp[ck-1][col] + (ld)(a)/(ld)(col) : (ld)oo),
(ck && col >= 2 ? dp[ck-1][col-1] + (ld)(b)/(ld)(col-1) : (ld)oo)
});
}
}
dp.swap(new_dp);
}
ld ans = oo;
for (int i = 1; i<=n; i++) ans = min(ans, dp[k][i]);
cout << fixed << setprecision(17) << ans << "\n";
}
int32_t main(){
ios_base::sync_with_stdio(0);
cin.tie(0);
cout.tie(0);
solve();
return 0;
}
