#include <bits/stdc++.h>

using namespace std;

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

int v[5000001];
int deq[5000001];

int main()
{
    int n,k;
    f>>n>>k;
    int i,j;
    for(i=1;i<=n;++i)
        f>>v[i];

    long long sum=0;
    long long st=1,dr=0;
    for(i=1;i<=n;i++)
    {
        while(st<=dr && v[i]<=v[deq[dr]])
            dr--;
        deq[++dr]=i;
        if(deq[st]==i-k)
            st++;
        if(i>=k)
            sum+=v[deq[st]];
    }
    g<<sum;
    return 0;
}