#include<cstdio>
#include<cstring>
#include<algorithm>
#include<cmath>
#include<ctime>
using namespace std;
int n,m,a[25];double s[25],dp[25][10],sum,ans=1e50;
double sqr(double x){return x*x;}
double getdp()
{
    for (int i=1;i<=n;++i) s[i]=s[i-1]+a[i];
    memset(dp,127,sizeof(dp));
    dp[0][0]=0;
    for (int i=1;i<=n;++i)
        for (int j=1;j<=m;j++)
            for (int k=0;k<i;k++)
                dp[i][j]=min(dp[i][j],dp[k][j-1]+sqr(s[i]-s[k]-sum));
    ans=min(ans,dp[n][m]);
    return dp[n][m];
}
double Rand(){return rand()%100000/100000.00;}
void SA(double T)
{
    double now=ans,nw;
    int x,y;
    while (T>1e-3)
    {
        int x=1+rand()%n,y=1+rand()%n;
        if (x==y) continue;
        swap(a[x],a[y]);
        nw=getdp();
        if (nw<now||exp((now-nw)/T)>Rand()) now=nw;
        else swap(a[x],a[y]);
        T*=0.99;
    }
}
int main()
{
    srand(141905+141936);
    scanf("%d %d",&n,&m);
    for (int i=1;i<=n;++i) scanf("%d",&a[i]),sum+=a[i];
    sum/=m;
    getdp();
    SA(1000);
    printf("%.2lf\n",sqrt(ans/m));
    return 0;
}