#include <fstream>
using namespace std;
ifstream f("deque.in");
ofstream g("deque.out");
int a[5000005],dq[5000005],fr,bk,n,k;
int main()
{
    long long s=0;
    f>>n>>k;
    fr=1;bk=0;
    for(int i=1;i<=n;i++)
        f>>a[i];
    for(int i=1;i<=n;i++)
    {
        while(fr<=bk && a[i]<=a[dq[bk]])bk--;
        dq[++bk]=i;
        if(dq[fr]==i-k)fr++;
        if(i>=k)s+=a[dq[fr]];
    }
    g<<s;
    return 0;
}