#include <iostream>
#include <fstream>

using namespace std;

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

long n,k,min1,s,a[5000001],st,dr,c[5000001],i,j;

int main()
{
    f>>n>>k;
    for(i=1;i<=n;i++)
    {
        f>>a[i];
    }
    st=1; dr=1;
    c[1]=1; s=0;
    for(i=2;i<=n;i++)
    {
        if(a[i]>=a[c[dr]])
        {
            dr=dr+1;
            c[dr]=i;
        }
        else
        {
            while(dr>=st && a[c[dr]]>a[i])
                dr=dr-1;
            c[++dr]=i;
        }

        if(i>=k)
           {
               s=s+a[c[st]];
               //cout<<a[c[st]]<<" ";
           }
        while(i-c[st]+1>=k)
            st=st+1;

    }
    g<<s;
    return 0;
}