#include<iostream>
#include<fstream>
#define ll long long

using namespace std;

ifstream f("deque.in");
ofstream g("deque.out");

int main()
{
    ll i,sum=0,n,k,min,j,pmin;
    f>>n>>k;
    ll a[n+1];
    for(i=1;i<=n;i++)
        f>>a[i];
    for(i=1;i<=n-k+1;i++)
    {
    if(i>1&&pmin>=i){
        if(a[pmin] < a[i+k-1])
            sum=sum+a[pmin];
        else
            sum=sum+a[i+k-1];
    }else
       {
         min =a[i];
        for(j=0;j<k;j++)
            if(min>a[j+i])
            {
                min=a[j+i];
                pmin=i+j;
            }

        sum=sum+min;
       }
       //cout<<min<<" ";
    }
    g<<sum;
    return 0;
}