#include <fstream>
#include <deque>
using namespace std;
ifstream cin("deque.in");
ofstream cout("deque.out");
const int NMAX = 5e6+1;
int n,x,k;
long long s;
int a[NMAX],dq[NMAX];
int f=1,b=0;
int main()
{
    cin>>n>>k;
    for(int i=1; i<=n; i++)
        cin>>a[i];
    for(int i=1; i<=n; i++)
    {
        while(f<=b &&  a[i]<=a[dq[b]])
            b--;
        dq[++b]=i;
        if(dq[f]==i-k)
            f++;
        if(i>=k)
            s+=a[dq[f]];
    }
    cout<<s;
    return 0;
}