#include <bits/stdc++.h>

using namespace std;

ifstream fin("deque.in");
ofstream fout("deque.out");

const int NMAX = 5000005;
int a[NMAX],deq[NMAX],n,k,st=1,dr;
long long sum=0;

int main()
{
    fin >> n >> k;
    for(int i=1;i<=n;i++){
        fin >> a[i];
        while(st<=dr and a[i]<=a[deq[dr]]) dr--;
        deq[++dr]=i;
        if(deq[st]==i-k) st++;
        if(i>=k) sum+=a[deq[st]];
    }
    fout << sum;
    return 0;
}