#include <fstream>

using namespace std;
ifstream fin("deque.in");
ofstream fout("deque.out");
long long v[5000001],int d[5000001];
int main()
{
    long long n,k,p,s,i,sum=0;
    fin>>n>>k;
    for(i=1;i<=n;i++)
    {
        fin>>v[i];

    }
    p=1;
    s=0;
    for(i=1;i<=n;i++)
    {
        while(p<=s&&v[i]<=v[d[s]])s--;
        d[++s]=i;
       if(d[p]==i-k)p++;
        if(i>=k)sum=sum+v[d[p]];

    }fout<<sum;

    return 0;
}