#include<fstream>


#define nmax 5000010

using namespace std;
ifstream cin("deque.in");
ofstream cout("deque.out");
int i, n, k;
int a[nmax], deque[nmax];
int front, back;
long long sum;
int main()
{
    cin>>n>>k;
    for(i=1; i<=n; i++)
    {
        cin>>a[i];
    }
    front=0, back=0;
    for(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)
        sum += a[deque[front] ];

    }
    cout<<sum;
    cin.close();
    cout.close();
    return 0;
}