#include <iostream>
#include <fstream>

using namespace std;
ifstream in("deque.in");
ofstream out("deque.out");

const int nmax=5000005;
int a[nmax],n,k,Deque[nmax];
long long s;
int main()
{
    in>>n>>k;
    for(int i=1;i<=n;i++)
        in>>a[i];
    int Front=1,Back=0;
    for(int i=1;i<=n;i++){
        while (Front <= Back&&a[i]<=a[Deque[Back]])
            Back--;
        Deque[++Back]=i;
        if (Deque[Front]==i-k)
            Front++;
        if (i>=k)
            s+=a[Deque[Front]];
        //cout<<s<<" ";
    }
    out<<s<<"\n";
    return 0;
}