#include<bits/stdc++.h>
using namespace std;
#define ll long long
#define int ll
#define pii pair<int, int>
#define ff first
#define ss second
#define ld long double
#define pb push_back
pair<ld, ld> a[300100];
ll b[300100];
ll us[300100];
ll n, m;
ld dp[600][600], ob[600][600];
bool cmp(int x, int y){
return a[x].ss < a[y].ss;
}
bool cmp2(pair<ld, ld> a, pair<ld, ld> b){
return a.ss < b.ss;
}
void solve(){
cin>>n>>m;
int cnt = 0;
vector<int> q;
for(int i=1; i<=n; i++){
cin>>a[i].ff>>a[i].ss;
if(a[i].ss == -1) a[i].ss = 1e9;
else cnt ++;
}
sort(a + 1, a + 1 + n, cmp2);
ld ans = 1e18;
for(int D=0; D<=n; D++){
for(int i=0; i<=n; i++){
for(int j=0; j<=n; j++){
dp[i][j] = ob[i][j] = 1e9;
}
}
dp[0][0] = 0;
for(int i=1; i<=n; i++){
for(int d=0; d<=n; d++){
for(int k=0; k<=n; k++){
ob[d][k] = min(ob[d][k], dp[d][k]);
ob[d][k + 1] = min(ob[d][k + 1], dp[d][k] + a[i].ff / (D + 1));
if(a[i].ss != 1e9) ob[d + 1][k + 1] = min(ob[d + 1][k + 1], dp[d][k] + a[i].ss / (d + 1));
}
}
for(int i=0; i<=n; i++){
for(int j=0; j<=n; j++){
dp[i][j] = ob[i][j];
ob[i][j] = 1e9;
}
}
}
ans = min(ans, dp[D][m]);
}
cout<<fixed<<setprecision(9)<<ans<<'\n';
}
signed main(){
solve();
}
