#include<bits/stdc++.h>
using namespace std;
using db=double;
using ll=long long;
const int N=2e5;
const db EPS=1e-9;
int n,m;
ll s[N+1];

pair<db,int> solve(db pen){
    auto C=[&](int l,int r){
        return sqrt((r-l)*(s[r]-s[l]))+pen;
    };
    static pair<db,int>dp[N+1];
    auto T=[&](int l,int r){
        return make_pair(dp[l].first+C(l,r),dp[l].second+1);
    };
    dp[0]={0,0};
    static pair<int,int>opt[N+1];
    int l=0,r=0;
    opt[r++]={1,0};
    for(int i=1;i<=n;i++){
        while(l+1<r&&opt[l+1].first<=i)l++;
        dp[i]=T(opt[l].second,i);
        while(r-l&&opt[r-1].first>i&&T(opt[r-1].second,opt[r-1].first)>T(i,opt[r-1].first))r--;
        if(l==r)opt[r++]={i+1,i};
        else{
            int low=max(i+1,opt[r-1].first),hi=n+1;
            while(low<hi){
                int mid=(low+hi)/2;
                T(i,mid)<T(opt[r-1].second,mid)?hi=mid:low=mid+1;
            }
            if(low<=n)opt[r++]={low,i};
        }
    }
    return dp[n];
}
int main(){
    cin.tie(0)->sync_with_stdio(0);
    cin>>n>>m;
    for(int i=1;i<=n;i++)cin>>s[i],s[i]+=s[i-1];
    db low=0,hi=1e18;
    while(hi-low>EPS){
        db mid=(low+hi)/2;
        auto[a,b]=solve(mid);
        b>=m?low=mid:hi=mid;
    }
    db x=(low+hi)/2;
    auto[a,b]=solve(x);
    cout<<fixed<<setprecision(12)<<a-x*m<<'\n';
}