#include <bits/stdc++.h>

using namespace std;
int v[5000005];
int main()
{
    ifstream cin("deque.in");
    ofstream cout("deque.out");
    int n,k,minn=2100000000,suma=0;
    cin>>n>>k;
    for(int i=0; i<n; i++)
        cin>>v[i];

    int j=k-1;
    for(int i=0; i<=n-k; i++)
    {
        //cout<<i<<" "<<v[i]<<" "<<v[j]<<'\n';
        ///i->k
        if(i==0)
        {
            for(int l=0; l<k; l++)
                minn=min(minn, v[l]);
        }
        else
        {
            if(v[j]<=minn)
                minn=v[j];
            else
            {
                minn=2100000000;
                for(int l=i; l<i+k; l++)
                    minn=min(minn, v[l]);
            }
        }
        suma+=minn;
        j++;
    }
    cout<<suma;


    return 0;
}