#include <fstream>
#define NM 5000001
using namespace std;
ifstream fin("deque.in");
ofstream fout("deque.out");
int n,k,a[NM],c[NM],p,u;
long long s;
int main()
{
    int i;
    fin>>n>>k;
     p=1;
    u=0;
    for(i=1; i<=n; i++)
    {
        fin>>a[i];

        while(p<=u && a[i]<=a[c[u]])
                {
                    c[u]=0;
                    u--;
                }

        u++;
        c[u]=i;

        if(c[p]==i-k)
            p++;

        if(i>=k)
            s=s+a[c[p]];
    }
fout<<s;
return 0;
}