#include <fstream>
using namespace std;
ifstream f("deque.in");
ofstream g("deque.out");
int k,i,n,st,dr;
long long s;
int main()
{
    f>>n>>k;
    int a[n+1],dq[n+1];
    for(i=1;i<=n;i++)
        f>>a[i];
    st=1;dr=1;
    dq[1]=1;
    for(i=2;i<=n;i++)
    {
        while(st<=dr&&a[i]<=a[dq[dr]])
            dr--;
        dq[++dr]=i;
        if(i-k==dq[st])
            st++;
        if(i>=k)
            s+=a[dq[st]];
    }
    g<<s;
    return 0;
}