#include <fstream>
using namespace std;
int deque[5000002],a[5000002];
int front,back;
int n,k,i;
long long sum;
int main()
{
    ifstream in("deque.in");
    ofstream out("deque.out");
    in>>n>>k;
    for(i=1;i<=n;i++)
    {
        in>>a[i];
    }
    front=1;
    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]];
    }
    out<<sum;
    return 0;
}